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Momentum distribution of a freely expanding Lieb-Liniger gas: We numerically study free expansion of a few Lieb-Liniger bosons, which are
initially in the ground state of an infinitely deep hard-wall trap. Numerical
calculation is carried out by employing a standard Fourier transform, as
follows from the Fermi-Bose transformation for a time-dependent Lieb-Liniger
gas. We study the evolution of the momentum distribution, the real-space
single-particle density, and the occupancies of natural orbitals. Our numerical
calculation allows us to explore the behavior of these observables in the
transient regime of the expansion, where they are non-trivially affected by the
particle interactions. We derive analytically (by using the stationary phase
approximation) the formula which connects the asymptotic shape of the momentum
distribution and the initial state. For sufficiently large times the momentum
distribution coincides (up to a simple scaling transformation) with the shape
of the real-space single-particle density (the expansion is asymptotically
ballistic). Our analytical and numerical results are in good agreement. | cond-mat_other |
Empirical Formula of the Absolute Value of Electrical Conductivity for
Elemental Metals and Its Interpretation By Fluctuation Dissipation Theorem: The absolute value of the electrical conductivity sigma of elemental metals
even at the room temperature range is not well theoretically understood. This
is particularly true in multivalent metals. This paper empirically found that
sigma=n_{atom}e^2tau0/mG with tau0=hbar/k_{B}T reproduces the observations
rather well for many metals as in Fig.1(b)-upper, if G is taken, by guessing to
be a summed number of electric bands counted from outer most orbitals. We find
by comparative study at the same time n_{atom}=n, namely Z=1 and m=m^* for
majority of metals for sigma. Thus the only quantity remained is tau. The
Bardeen's tau is found equal to tau0 if the deformation potential is equal to
Fermi energy, using the observationally ascertained fact that thermal acoustic
energy=the Fermi energy. Since electrons behave nearly as free electrons, the
wave function should show the minimum uncertainty relation of Delta p_{x}
Delta_{x}=hbar/2, which following the classical Fluctuation-Dissipation-Theorem
shows in fact tau0=hbar/k_{B}T. | cond-mat_other |
On Entropy Wind in Superfluid Helium: Generation of a quasi-stationary flow of the superfluid helium normal part in
the presence of intense first- and second-sound waves is studied. Relevant
equations are obtained. The contribution to the process of energy dissipation
at the shock front layer and of fluid viscosity is analysed in detail for the
case of a second-sound wave. An estimate concerning possible experimental
observation of the process is made. | cond-mat_other |
Magnetic vortex nucleation/annihilation in artificial-ferrimagnet
microdisks: The topological nature of magnetic-vortex state gives rise to peculiar
magnetization reversal observed in magnetic microdisks. Interestingly,
magnetostatic and exchange energies which drive this reversal can be
effectively controlled in artificial ferrimagnet heterostructures composed of
rare-earth and transition metals. 25x[Py(t)/Gd(t)] (t=1 or 2 nm) superlattices
demonstrate a pronounced change of the magnetization and exchange stiffness in
a 10-300 K temperature range as well as very small magnetic anisotropy. Due to
these properties, the magnetization of cylindrical microdisks composed of these
artificial ferrimagnets can be transformed from the vortex to
uniformly-magnetized states in a permanent magnetic field by changing the
temperature. We explored the behavior of magnetization in 1.5-micrometer
25x[Py(t)/Gd(t)] (t=1 or 2 nm) disks at different temperatures and magnetic
fields and observed that due to the energy barrier separating vortex and
uniformly-magnetized states, the vortex nucleation and annihilation occur at
different temperatures. This causes the temperature dependences of the Py/Gd
disks magnetization to demonstrate unique hysteretic behavior in a narrow
temperature range. It was discovered that for the 25x[Py(2 nm)/Gd(2 nm)]
microdisks the vortex can be metastable at a certain temperature range. | cond-mat_other |
Experimental determination of the dipolar field in Mn12-acetate: Crystals of the molecular magnet Mn12-acetate are known to contain a small
fraction of low- symmetry (minor) species with a small anisotropy barrier
against spin reversal. The lower barrier leads to faster magnetic relaxation
and lower coercive field. We exploit the low coercive fields of the minor
species to make a direct determination of the dipole field in Mn12-ac. We find
that the dipolar field of a fully magnetized crystal is 51.5 \pm 8.5 mT,
consistent with theoretical expectations. | cond-mat_other |
NMR in $^3$He-B: This text contains a collection of equations useful for understanding Nuclear
Magnetic Resonance (NMR) experiments in superfluid $^3$He-B. This is a part of
my notebook where I try to describe some parts of this sophisticated system. | cond-mat_other |
Propagation of self-localised Q-ball solitons in the $^3$He universe: In relativistic quantum field theories, compact objects of interacting bosons
can become stable owing to conservation of an additive quantum number $Q$.
Discovering such $Q$-balls propagating in the Universe would confirm
supersymmetric extensions of the standard model and may shed light on the
mysteries of dark matter, but no unambiguous experimental evidence exists. We
report observation of a propagating long-lived $Q$-ball in superfluid $^3$He,
where the role of $Q$-ball is played by a Bose-Einstein condensate of magnon
quasiparticles. We achieve accurate representation of the $Q$-ball Hamiltonian
using the influence of the number of magnons, corresponding to the charge $Q$,
on the orbital structure of the superfluid $^3$He order parameter. This
realisation supports multiple coexisting $Q$-balls which in future allows
studies of $Q$-ball dynamics, interactions, and collisions. | cond-mat_other |
Stroboscopic aliasing in long-range interacting quantum systems: We unveil a mechanism for generating oscillations with arbitrary multiplets
of the period of a given external drive, in long-range interacting quantum
many-particle spin systems. These oscillations break discrete time translation
symmetry as in time crystals, but they are understood via two intertwined
stroboscopic effects similar to the aliasing resulting from video taping a
single fast rotating helicopter blade. The first effect is similar to a single
blade appearing as multiple blades due to a frame rate that is in resonance
with the frequency of the helicopter blades' rotation; the second is akin to
the optical appearance of the helicopter blades moving in reverse direction.
Analogously to other dynamically stabilized states in interacting quantum
many-body systems, this stroboscopic aliasing is robust to detuning and
excursions from a chosen set of driving parameters, and it offers a novel route
for engineering dynamical $n$-tuplets in long-range quantum simulators, with
potential applications to spin squeezing generation and entangled state
preparation. | cond-mat_other |
Excitons in long molecular chains near the reflecting interface: We discuss coherent exciton-polariton states in long molecular chains that
are formed due to the interaction of molecular excitations with both vacuum
photons and surface excitations of the neighboring reflecting substrate. The
resonance coupling with surface plasmons (or surface polaritons) of the
substrate can substantially contribute to the retarded intermolecular
interactions leading to an efficient channel of the decay of one-dimensional
excitons with small momenta via emission of surface excitations. The interface
also modifies the radiative decay of excitons into vacuum photons. In an
idealized system, excitons with higher momenta would not emit photons nor
surface waves. For a dissipative substrate, additional exciton quenching takes
place owing to Joule losses as the electric field of the exciton polarization
penetrates the substrate. We discuss how these effects depend on the
polarization of molecular excitations, their frequency and on the distance of
the chain from the substrate. | cond-mat_other |
Electronic properties of ordered and disordered linear clusters of atoms
and molecules: The electronic properties of one-dimensional clusters of N atoms or molecules
have been studied. The model used is similar to the Kronig-Penney model with
the potential offered by each ion being approximated by an attractive delta
function. The energy eigenvalues, the eigenstates and the density of states are
calculated exactly for a linear cluster of N atoms or molecules. The dependence
of these quantities on the various parameters of the problem show interesting
behavior. Effects of random distribution of the positions of the atoms and
random distribution of the strengths of the potential have also been studied.
The results obtained in this paper can have direct applications for linear
chain of atoms produced on metal surfaces or artificially created chain of
atoms by using scanning tunneling microscope or in studying molecular
conduction of electrons across one-dimensional barriers. | cond-mat_other |
Thermodynamically consistent equilibrium properties of normal-liquid
Helium-3: The high-precision data for the specific heat C_{V}(T,V) of normal-liquid
Helium-3 obtained by Greywall, taken together with the molar volume V(T_0,P) at
one temperature T_0, are shown to contain the complete thermodynamic
information about this phase in zero magnetic field. This enables us to
calculate the T and P dependence of all equilibrium properties of normal-liquid
Helium-3 in a thermodynamically consistent way for a wide range of parameters.
The results for the entropy S(T,P), specific heat at constant pressure
C_P(T,P), molar volume V(T,P), compressibility kappa(T,P), and thermal
expansion coefficient alpha(T,P) are collected in the form of figures and
tables. This provides the first complete set of thermodynamically consistent
values of the equilibrium quantities of normal-liquid Helium-3. We find, for
example, that alpha(T,P) has a surprisingly intricate pressure dependence at
low temperatures, and that the curves alpha(T,P) vs T do not cross at one
single temperature for all pressures, in contrast to the curves presented in
the comprehensive survey of helium by Wilks.
Corrected in cond-mat/9906222v3: The sign of the coefficient d_0 was
misprinted in Table I of cond-mat/9906222v1 and v2. It now correctly reads
d_0=-7.1613436. All results in the paper were obtained with the correct value
of d_0. (We would like to thank for E. Collin, H. Godfrin, and Y. Bunkov for
finding this misprint.) | cond-mat_other |
Three comments on the Fermi gas at unitarity in a harmonic trap: In this note we consider three issues related to the unitary Fermi gas in a
harmonic trap. We present a short proof of a virial theorem, which states that
the average energy of a particle system at unitarity in a harmonic trap is
twice larger than the average potential energy. The theorem is valid for all
systems with no intrinsic scale, at zero or finite temperature. We discuss the
odd-even splitting in a unitarity Fermi gas in a harmonic trap. We show that at
large number of particles N the odd-even splitting is proportional to
N^{1/9}\hbar\omega, with an undetermined numerical constant. We also show that
for odd N the lowest excitation energies are of order N^{-1/3}\hbar\omega. | cond-mat_other |
Measurements on Melting Pressure, Metastable Solid Phases, and Molar
Volume of Univariant Saturated Helium Mixture: A concentration-saturated helium mixture at the melting pressure consists of
two liquid phases and one or two solid phases. The equilibrium system is
univariant, whose properties depend uniquely on temperature. Four coexisting
phases can exist on singular points, which are called quadruple points. As a
univariant system, the melting pressure could be used as a thermometric
standard. It would provide some advantages compared to the current reference,
namely pure $^3$He, especially at the lowest temperatures below 1 mK. We have
extended the melting pressure measurements of the concentration-saturated
helium mixture from 10 mK to 460 mK. The density of the dilute liquid phase was
also recorded. The effect of the equilibrium crystal structure changing from
hcp to bcc was clearly seen at T=294 mK at the melting pressure P=2.638 MPa. We
observed the existence of metastable solid phases around this point. No
evidence was found for the presence of another, disputed, quadruple point at
around 400 mK. The experimental results agree well with our previous
calculations at low temperatures, but deviate above 200 mK. | cond-mat_other |
Theory of Forces Induced by Evanescent Fields: We present the theoretical foundations of the interaction of electromagnetic
evanescent fields on an object | cond-mat_other |
Anomalous Hall conductivity: local orbitals approach: A theory of the anomalous Hall conductivity based on the properties of single
site orbitals is presented. Effect of the finite electron life time is modeled
by energy fluctuations of atomic-like orbitals. Transition from the ideal Bloch
system for which the conductivity is determined by the Berry phase curvatures
to the case of strong disorder for which the conductivity becomes dependent on
the relaxation time is analyzed. Presented tight-binding model gives by the
unified way experimentally observed qualitative features of the anomalous
conductivity in the so called good metal regime and that called as bad metal or
hopping regime. | cond-mat_other |
Photon transport in a dissipative chain of nonlinear cavities: We analyze a chain of coupled nonlinear optical cavities driven by a coherent
source of light localized at one end and subject to uniform dissipation. We
characterize photon transport by studying the populations and the photon
correlations as a function of position. When complemented with input-output
theory, these quantities provide direct information about photon transmission
through the system. The position of single- and multi-photon resonances
directly reflect the structure of the many-body energy levels. This shows how a
study of transport along a coupled cavity array can provide rich information
about the strongly correlated (many-body) states of light even in presence of
dissipation. By means of a numerical algorithm based on the time-evolving block
decimation scheme adapted to mixed states, we are able to simulate arrays up to
sixty cavities. | cond-mat_other |
The Effect Of Delay Times On The Optimal Velocity Traffic Flow Behavior: We have numerically investigated the effect of the delay times $\tau_f$ and
$\tau_s$ of a mixture of fast and slow vehicles on the fundamental diagram of
the optimal velocity model. The optimal velocity function of the fast cars
depends not only on the headway of each car but also on the headway of the
immediately preceding one. It is found that the small delay times have almost
no effects, while, for sufficiently large delay time $\tau_s$ the current
profile displays qualitatively five different forms depending on $\tau_f$,
$\tau_s$ and the fractions $d_f$ and $d_s$ of the fast and slow cars
respectively. The velocity (current) exhibits first order transitions at low
and/or high densities, from freely moving phase to the congested state, and
from congested state to the jamming one respectively accompanied by the
existence of a local minimal current. Furthermore, there exist a critical value
of $\tau_f$ above which the metastability and hysteresis appear. The
spatial-temporal traffic patterns present more complex structure | cond-mat_other |
Generalized Mean Field Approach to a Resonant Bose-Fermi Mixture: We formulate a generalized mean-field theory of a mixture of fermionic and
bosonic atoms, in which the fermion-boson interaction can be controlled by a
Feshbach resonance. The theory correctly accounts for molecular binding
energies of the molecules in the two-body limit, in contrast to the most
straightforward mean-field theory. Using this theory, we discuss the
equilibrium properties of fermionic molecules created from atom pairs in the
gas. We also address the formation of molecules when the magnetic field is
ramped across the resonance, and present a simple Landau-Zener result for this
process. | cond-mat_other |
Statics and dynamics of BEC's in double square well potentials: In this paper we treat the behavior of Bose Einstein condensates in double
square well potentials, both of equal and different depths. For even depth,
symmetry preserving solutions to the relevant nonlinear Schr\"{o}dinger
equation is known, just as in the linear limit. When the nonlinearity is strong
enough, symmetry breaking solutions also exist, side by side with the symmetric
one. Interestingly, solutions almost entirely localized in one of the wells are
known as an extreme case. Here we outline a method for obtaining all these
solutions for repulsive interactions. The bifurcation point at which, for
critical nonlinearity, the asymmetric solutions branch off from the symmetry
preserving ones is found analytically. We also find this bifurcation point and
treat the solutions generally via a Josephson Junction model.
When the confining potential is in the form of two wells of different depth,
interesting new phenomena appear. This is true of both the occurrence of the
bifurcation point for the static solutions, and also of the dynamics of phase
and amplitude varying solutions. Again a generalization of the Josephson model
proves useful. The stability of solutions is treated briefly. | cond-mat_other |
Dynamical instability and domain formation in a spin-1 Bose condensate: We interpret the recently observed spatial domain formation in spin-1 atomic
condensates as a result of dynamical instability. Within the mean field theory,
a homogeneous condensate is dynamically unstable (stable) for ferromagnetic
(antiferromagnetic) atomic interactions. We find this dynamical instability
naturally leads to spontaneous domain formation as observed in several recent
experiments for condensates with rather small numbers of atoms. For trapped
condensates, our numerical simulations compare quantitatively to the
experimental results, thus largely confirming the physical insight from our
analysis of the homogeneous case. | cond-mat_other |
Classical and quantum dynamics of a model for atomic-molecular
Bose--Einstein condensates: We study a model for a two-mode atomic-molecular Bose--Einstein condensate.
Starting with a classical analysis we determine the phase space fixed points of
the system. It is found that bifurcations of the fixed points naturally
separate the coupling parameter space into four regions. The different regions
give rise to qualitatively different dynamics. We then show that this
classification holds true for the quantum dynamics. | cond-mat_other |
Modelling turbulent flow of superfluid $^4$He past a rough solid wall in
the $T = 0$ limit: We present a numerical study, using the vortex filament model, of vortex
tangles in a flow of pure superfluid $^4$He in the $T = 0$ limit through a
channel of width $D = 1$ mm for various applied velocities $V$. The flat
channel walls are assumed to be microscopically rough such that vortices
terminating at the walls are permanently pinned; vortices are liberated from
their pinned ends exclusively through self-reconnection with their images.
Sustained tangles were observed, for a period of 80 s, above the critical
velocity $V_c \sim 0.20$ cm s$^{-1} = 20 \kappa/D$. The coarse-grained velocity
profile was akin to a classical parabolic profile of the laminar Poiseuille
flow, albeit with a non-zero slip velocity $\sim$ 0.20 cm s$^{-1}$ at the
walls. The friction force was found to be proportional to the applied velocity.
The effective kinematic viscosity was $\sim 0.1\kappa$, and effective Reynolds
numbers within $\mathrm{Re'} < 15$. The fraction of the polarized vortex length
varied between zero in the middle of the channel and $\sim$ 60% within the
shear flow regions $\sim D/4$ from the walls. Therefore, we studied a state of
polarized ultraquantum (Vinen) turbulence fuelled at short lengthscales by
vortex reconnections, including those with vortex images due to the relative
motion between the vortex tangle and the pinning rough surface. | cond-mat_other |
Scanning optical homodyne detection of high-frequency picoscale
resonances in cantilever and tuning fork sensors: Higher harmonic modes in nanoscale silicon cantilevers and microscale quartz
tuning forks are detected and characterized using a custom scanning optical
homodyne interferometer. Capable of both mass and force sensing, these
resonators exhibit high-frequency harmonic motion content with picometer-scale
amplitudes detected in a 2.5 MHz bandwidth, driven by ambient thermal
radiation. Quartz tuning forks additionally display both in-plane and
out-of-plane harmonics. The first six electronically detected resonances are
matched to optically detected and mapped fork eigenmodes. Mass sensing
experiments utilizing higher tuning fork modes indicate >6x sensitivity
enhancement over fundamental mode operation. | cond-mat_other |
A model for luminescence of localized state ensemble: A distribution function for localized carriers,
$f(E,T)=\frac{1}{e^{(E-E_a)/k_BT}+\tau_{tr}/\tau_r}$, is proposed by solving a
rate equation, in which, electrical carriers' generation, thermal escape,
recapture and radiative recombination are taken into account. Based on this
distribution function, a model is developed for luminescence from localized
state ensemble with a Gaussian-type density of states. The model reproduces
quantitatively all the anomalous temperature behaviors of localized state
luminescence. It reduces to the well-known band-tail and luminescence quenching
models under certain approximations. | cond-mat_other |
The constitutive tensor of linear elasticity: its decompositions, Cauchy
relations, null Lagrangians, and wave propagation: In linear anisotropic elasticity, the elastic properties of a medium are
described by the fourth rank elasticity tensor C. The decomposition of C into a
partially symmetric tensor M and a partially antisymmetric tensors N is often
used in the literature. An alternative, less well-known decomposition, into the
completely symmetric part S of C plus the reminder A, turns out to be
irreducible under the 3-dimensional general linear group. We show that the
SA-decomposition is unique, irreducible, and preserves the symmetries of the
elasticity tensor. The MN-decomposition fails to have these desirable
properties and is such inferior from a physical point of view. Various
applications of the SA-decomposition are discussed: the Cauchy relations
(vanishing of A), the non-existence of elastic null Lagrangians, the
decomposition of the elastic energy and of the acoustic wave propagation. The
acoustic or Christoffel tensor is split in a Cauchy and a non-Cauchy part. The
Cauchy part governs the longitudinal wave propagation. We provide explicit
examples of the effectiveness of the SA-decomposition. A complete class of
anisotropic media is proposed that allows pure polarizations in arbitrary
directions, similarly as in an isotropic medium. | cond-mat_other |
Transmodal Fabry-Pérot Resonance: Theory and Realization with Elastic
Metamaterials: We discovered a new transmodal Fabry-P\'erot resonance that one elastic-wave
mode is maximally transmitted to another when the phase difference of two
dissimilar modes through an anisotropic layer is exactly odd multiples of
{\pi}. Unlike the well-established Fabry-P\'erot resonance, the transmodal
resonance must involve two coupled elastic-wave modes, longitudinal and shear.
The formation of wiggly transmodal transmission spectra is due to structural
instability appearing in anisotropic mode-coupled elastic-media. Experiments
with elastic metamaterials confirmed our findings which can play a critical
role in shear-mode ultrasound applications. | cond-mat_other |
A priori Wannier functions from modified Hartree-Fock and Kohn-Sham
equations: The Hartree-Fock equations are modified to directly yield Wannier functions
following a proposal of Shukla et al. [Chem. Phys. Lett. 262, 213-218 (1996)].
This approach circumvents the a posteriori application of the Wannier
transformation to Bloch functions. I give a novel and rigorous derivation of
the relevant equations by introducing an orthogonalizing potential to ensure
the orthogonality among the resulting functions. The properties of these,
so-called a priori Wannier functions, are analyzed and the relation of the
modified Hartree-Fock equations to the conventional, Bloch-function-based
equations is elucidated. It is pointed out that the modified equations offer a
different route to maximally localized Wannier functions. Their computational
solution is found to involve an effort that is comparable to the effort for the
solution of the conventional equations. Above all, I show how a priori Wannier
functions can be obtained by a modification of the Kohn-Sham equations of
density-functional theory. | cond-mat_other |
Threshold for Chaos and Thermalization in One-Dimensional Mean-Field
Bose-Hubbard Model: We study the threshold for chaos and its relation to thermalization in the 1D
mean-field Bose-Hubbard model, which in particular describes atoms in optical
lattices. We identify the threshold for chaos, which is finite in the
thermodynamic limit, and show that it is indeed a precursor of thermalization.
Far above the threshold, the state of the system after relaxation is governed
by the usual laws of statistical mechanics. | cond-mat_other |
Thermodynamic Measurements in a Strongly Interacting Fermi Gas: We conduct a series of measurements on the thermodynamic properties of an
optically-trapped strongly interacting Fermi gas, including the energy $E$,
entropy $S$, and sound velocity $c$. Our model-independent measurements of $E$
and $S$ enable a precision study of the finite temperature thermodynamics. The
$E(S)$ data are directly compared to several recent predictions. The
temperature in both the superfluid and normal fluid regime is obtained from the
fundamental thermodynamic relation $T=\partial E/\partial S$ by parameterizing
the $E(S)$ data. Our $E(S)$ data are also used to experimentally calibrate the
endpoint temperatures obtained for adiabatic sweeps of the magnetic field
between the ideal and strongly interacting regimes. This enables the first
experimental calibration of the temperature scale used in experiments on
fermionic pair condensation. Our calibration shows that the ideal gas
temperature measured for the onset of pair condensation corresponds closely to
the critical temperature estimated in the strongly interacting regime from the
fits to our $E(S)$ data. The results are in very good agreement with recent
predictions. Finally, using universal thermodynamic relations, we estimate the
chemical potential and heat capacity of the trapped gas from the $E(S)$ data. | cond-mat_other |
Shear-strain-induced Spatially Varying Super-lattice Structures on
Graphite studied by STM: We report on the Scanning Tunneling Microscope (STM) observation of linear
fringes together with spatially varying super-lattice structures on (0001)
graphite (HOPG) surface. The structure, present in a region of a layer bounded
by two straight carbon fibers, varies from a hexagonal lattice of 6nm
periodicity to nearly a square lattice of 13nm periodicity. It then changes
into a one-dimensional (1-D) fringe-like pattern before relaxing into a
pattern-free region. We attribute this surface structure to a shear strain
giving rise to a spatially varying rotation of the affected graphite layer
relative to the bulk substrate. We propose a simple method to understand these
moire patterns by looking at the fixed and rotated lattices in the Fourier
transformed k-space. Using this approach we can reproduce the spatially varying
2-D lattice as well as the 1-D fringes by simulation. The 1-D fringes are found
to result from a particular spatial dependence of the rotation angle. | cond-mat_other |
Highly sensitive and broadband carbon nanotube radio-frequency
single-electron transistor: We have investigated radio-frequency single-electron transistor (RF-SET)
operation of single-walled carbon nanotube quantum dots in the strong tunneling
regime. At 4.2 K and carrier frequency 754.2 MHz, we reach a charge sensitivity
of 2.3e-6 e/Hz^(1/2) over a bandwidth of 85 MHz. Our results indicate a
gain-bandwidth product of 3.7e13 Hz^(3/2)/e, which is by one order of magnitude
better than for typical RF-SETs. | cond-mat_other |
Counterflow quantum turbulence in a square channel under the normal
fluid with a Poiseuille flow: We perform a numerical analysis of superfluid turbulence produced by thermal
counterflow in He II by using the vortex filament model. Counterflow in a low
aspect ratio channel is known to show the transition from laminar flow to the
two turbulent states TI and TII. The present understanding is that the TI has
the turbulent superfluid and the laminar normal fluid but both fluids are
turbulent in the TII state. This work studies the vortex tangle in the TI
state. Solid boundary condition is applied to walls of a square channel, and
the velocity field of the normal fluid is prescribed to be a laminar Poiseuille
profile. An inhomogeneous vortex tangle, which concentrates near the solid
boundaries, is obtained as the statistically steady state. It is sustained by
its characteristic space-time oscillation. The inhomogeneity of the vortex
tangle shows the characteristic dependence on temperature, which is caused by
two competitive effects, namely the profile of the counterflow velocity and the
mutual friction. | cond-mat_other |
A new ripplon branch in He II: We analyse the dispersion relation of ripplons, on the surface of superfluid
helium, using the dispersive hydrodynamics approach and find a new ripplon
branch. We obtain analytical equation for the dispersion relation and analytic
expressions for the limiting cases. We discuss where ripplons can exist in the
energy-wavenumber plane. A numerical solution for the ripplon dispersion curve
is obtained in the allowed regions. The new ripplon branch is found at energies
just below the instability point. | cond-mat_other |
Strong magnetic coupling between an electronic spin qubit and a
mechanical resonator: We describe a technique that enables a strong, coherent coupling between a
single electronic spin qubit associated with a nitrogen-vacancy impurity in
diamond and the quantized motion of a magnetized nano-mechanical resonator tip.
This coupling is achieved via careful preparation of dressed spin states which
are highly sensitive to the motion of the resonator but insensitive to
perturbations from the nuclear spin bath. In combination with optical pumping
techniques, the coherent exchange between spin and motional excitations enables
ground state cooling and the controlled generation of arbitrary quantum
superpositions of resonator states. Optical spin readout techniques provide a
general measurement toolbox for the resonator with quantum limited precision. | cond-mat_other |
The cold atom Hubbard toolbox: We review recent theoretical advances in cold atom physics concentrating on
strongly correlated cold atoms in optical lattices. We discuss recently
developed quantum optical tools for manipulating atoms and show how they can be
used to realize a wide range of many body Hamiltonians. Then we describe
connections and differences to condensed matter physics and present
applications in the fields of quantum computing and quantum simulations.
Finally we explain how defects and atomic quantum dots can be introduced in a
controlled way in optical lattice systems. | cond-mat_other |
Higher-order vortex solitons, multipoles, and supervortices on a square
optical lattice: We predict new generic types of vorticity-carrying soliton complexes in a
class of physical systems including an attractive Bose-Einstein condensate in a
square optical lattice (OL) and photonic lattices in photorefractive media. The
patterns include ring-shaped higher-order vortex solitons and supervortices.
Stability diagrams for these patterns, based on direct simulations, are
presented. The vortex ring solitons are stable if the phase difference \Delta
\phi between adjacent solitons in the ring is larger than \pi/2, while the
supervortices are stable in the opposite case, \Delta \phi <\pi /2. A
qualitative explanation to the stability is given. | cond-mat_other |
Bose-Einstein condensate in a quartic potential: Static and Dynamic
properties: In this paper, we present a theoretical study of a Bose-Einstein condensate
of interacting bosons in a quartic trap in one, two, and three dimensions.
Using Thomas-Fermi approximation, suitably complemented by numerical solutions
of the Gross-Pitaevskii equation, we study the ground sate condensate density
profiles, the chemical potential, the effects of cross-terms in the quartic
potential, temporal evolution of various energy components of the condensate,
and width oscillations of the condensate. Results obtained are compared with
corresponding results for a bose condensate in a harmonic confinement. | cond-mat_other |
Optical Tamm states in one-dimensional magnetophotonic structures: We demonstrate the existence of a spectrally narrow localized surface state,
the so-called optical Tamm state, at the interface between a 1D magnetophotonic
and non-magnetic photonic crystals. The state is spectrally located inside the
photonic band gaps of each of the photonic crystals comprising this
magnetophotonic structure. This state is associated with a sharp transmission
peak through the sample and is responsible for the substantial enhancement of
the Faraday rotation for the corresponding wavelength. The experimental results
are in excellent agreement with the theoretical predictions. | cond-mat_other |
Quasiparticle universes in Bose-Einstein condensates: Recent developments in simulating fundamental quantum field theoretical
effects in the kinematical context of analogue gravity are reviewed.
Specifically, it is argued that a curved space-time generalization of the
Unruh-Davies effect -- the Gibbons-Hawking effect in the de Sitter space-time
of inflationary cosmological models -- can be implemented and verified in an
ultracold gas of bosonic atoms. | cond-mat_other |
Evaporative Cooling of a Photon Fluid to Quantum Degeneracy: We demonstrate that the process of evaporative cooling, as associated with
the cooling of atomic gases, can also be employed to condense a system of
photons giving rise to coherent properties of the light. The system we study
consists of photons in a high-quality Fabry-Perot cavity with photon
interactions mediated by a nonlinear atomic medium. We predict a macroscopic
occupation of the lowest energy mode and evaluate the conditions for realizing
a narrow spectral width indicative of a long coherence time for the field. | cond-mat_other |
Entangling two defects via a surrounding crystal: We theoretically show how two impurity defects in a crystalline structure can
be entangled through coupling with the crystal. We demonstrate this with a
harmonic chain of trapped ions in which two ions of a different species are
embedded. Entanglement is found for sufficiently cold chains and for a certain
class of initial, separable states of the defects. It results from the
interplay between localized modes which involve the defects and the interposed
ions, it is independent of the chain size, and decays slowly with the distance
between the impurities. These dynamics can be observed in systems exhibiting
spatial order, viable realizations are optical lattices, optomechanical
systems, or cavity arrays in circuit QED. | cond-mat_other |
Quantum oscillations in a two-mode atom-molecule Bose-Einstein
condensate -- the discrete WKB approach: Quantum effects in a system of coupled atomic and molecular Bose-Einstein
condensates in the framework of a two-mode model are studied numerically and
analytically, using the discrete WKB approach. In contrast to the mean-field
approximation, the WKB analytical results are in a very good agreement with
numerical results. The quantum fluctuations of the atomic and molecular
populations are calculated, and found to be of the same order of magnitude as
their mean values. | cond-mat_other |
Radial quadrupole and scissors modes in trapped Fermi gases across the
BCS phase transition: The excitation spectra of the radial quadrupole and scissors modes of
ultracold Fermi gases in elongated traps are studied across the BCS
superfluid-normal phase transition in the framework of a transport theory for
quasiparticles. In the limit of zero temperature, this theory reproduces the
results of superfluid hydrodynamics, while in the opposite limit, above the
critical temperature, it reduces to the collisionless Vlasov equation. In the
intermediate temperature range, the excitation spectra have two or three broad
peaks, respectively, which are roughly situated at hydrodynamic and
collisionless frequencies, and whose strength is shifted from the hydrodynamic
to the collisionless modes with increasing temperature. By fitting the time
dependent quadrupole deformation with a damped oscillation of a single
frequency, we can understand the "jump" of the frequency of the radial
quadrupole mode as a function of interaction strength which has recently been
reported by the Innsbruck group. | cond-mat_other |
Hall Viscosity and the Acoustic Faraday Effect: For more than 20 years, observation of the non-dissipative Hall viscosity in
the quantum Hall effect has been impeded by the difficulty to probe directly
the momentum of the two-dimensional electron gas. However, in three-dimensional
systems such as superfluid ${}^{3}\mathrm{He}\!\!-\!\!\mathrm{B}$, the momentum
density is readily probed through transverse acoustic waves. We show that in a
three-dimensional elastic medium supporting transverse waves, a non-vanishing
Hall viscosity induces circular birefringence. Such an effect has been observed
in ${}^{3}\mathrm{He}\!\!-\!\!\mathrm{B}$ in the presence of a weak magnetic
field, and is known as the acoustic Faraday effect. The acoustic Faraday effect
has been understood in terms of the Zeeman splitting of the excited order
parameter modes which support the transverse wave propagation in the
superfluid. We show that the Zeeman effect can generically lead to a non-zero
Hall viscosity coefficient, and confirm this prediction using a simple
phenomenological model for the ${}^{3}\mathrm{He}\!\!-\!\!\mathrm{B}$
collective modes. Therefore, we claim that the observation of the acoustic
Faraday effect can be leveraged to make a direct observation of the Hall
viscosity in superfluid ${}^{3}\mathrm{He}\!\!-\!\!\mathrm{B}$ in a magnetic
field and other systems such as the crystalline
$\mathrm{Tb}_{3}\mathrm{Ga}_{5}\mathrm{O}_{12}$ material. | cond-mat_other |
A simple model of Feshbach molecules: We present a two-channel model to describe the quantum state of two atoms
with finite-range interaction near a Feshbach resonance. This model provides a
simple picture to analytically derive the wave function and the binding energy
of the molecular bound state. The results agree excellently with the
measurements and multichannel calculations. For small binding energies, the
system enters a threshold regime in which the Feshbach molecules are identical
to long range atom pairs in single channel. According to their threshold
behavior, we find Feshbach resonances can be classified into two types. | cond-mat_other |
N-particle Bogoliubov vacuum state: We consider the Bogoliubov vacuum state in the number-conserving Bogoliubov
theory proposed by Castin and Dum [Phys. Rev. A 57, 3008 (1998)]. We show that
in the particle representation the vacuum can be written in a simple diagonal
form. The vacuum state can describe the stationary N-particle ground state of a
condensate in a trap, but it can also represent a dynamical state when, for
example, a Bose-Einstein condensate initially prepared in the stationary ground
state is subject to a time-dependent perturbation. In both cases the diagonal
form of the Bogoliubov vacuum can be obtained by basically diagonalizing the
reduced single particle density matrix of the vacuum. We compare N-body states
obtained within the Bogoliubov theory with the exact ground states in a 3-site
Bose-Hubbard model. In this example, the Bogoliubov theory fails to accurately
describe the stationary ground state in the limit when N goes to infinity but a
small fraction of depleted particles is kept constant. | cond-mat_other |
A simple variational approach for an interacting Fermi trapped gas: Quantum states of a two-component Fermi trapped gas are described by
introducing an effective trap frequency, determined via variational techniques.
Closed expressions for the contribution of a contact interaction potential to
the total energy and the pairing interaction are derived. They are valid for
both few and large number of particles, given the discrete nature of the
formulation, and therefore richer than the continuous expressions, which are
perfectly matched. Pairing energies within a shell are explicitly evaluated and
its allowed values at a given energy level delimited. We show the importance of
the interaction over the trap energy as the number of particles ($N$) grows and
the temperature decreases. At zero temperature we find a polynomial dependence
of the interaction energy on the Fermi energy, whose dominant term at large $N$
corresponds with the mean field approximation result. In addition, the role of
the strength of an attractive potential on the total energy is exhibited. | cond-mat_other |
Implications of experimental probes of the RG-flow in quantum Hall
systems: We review the implications of the scaling data for the emergent symmetry of
the quantum Hall system. The location of the fixed points in the conductivity
plane is consistent with the global, non-Abelian discrete symmetry $\Gamma
_{0}(2)$, and the renormalisation group (RG) flow-lines agree closely with that
found if the symmetry acts anti-holomorphically. We extend the analysis to
consider the rate of the RG flow. For a specific model in which the $\Gamma
_{0}(2)$ symmetry acts anti-holomorphically the scaling close to the fixed
points gives a critical delocalisation exponent $\nu = 2.38\pm 0.02$, in
excellent greement with direct measurements and with numerical simulations.
Both the predicted flow-lines and the flow rate also agree with the
experimental measurements far away from the critical points, suggesting an
emergent topological structure capable of stabilising the symmetry predictions.
We hope that this agreement will stimulate further experimental study capable
of conclusively testing the symmetry and exploring its associated dynamics. | cond-mat_other |
Entangling two defects via a surrounding crystal: We theoretically show how two impurity defects in a crystalline structure can
be entangled through coupling with the crystal. We demonstrate this with a
harmonic chain of trapped ions in which two ions of a different species are
embedded. Entanglement is found for sufficiently cold chains and for a certain
class of initial, separable states of the defects. It results from the
interplay between localized modes which involve the defects and the interposed
ions, it is independent of the chain size, and decays slowly with the distance
between the impurities. These dynamics can be observed in systems exhibiting
spatial order, viable realizations are optical lattices, optomechanical
systems, or cavity arrays in circuit QED. | cond-mat_other |
Sound velocities of hexagonal close-packed H2 and He under pressure: Bulk, shear, and compressional aggregate sound velocities of hydrogen and
helium in the close- packed hexagonal structure are calculated over a wide
pressure range using two complementary approaches: semi-empirical lattice
dynamics based on the many-body intermolecular potentials and
density-functional theory in the generalized gradient approximation. The sound
velocities are used to calculate pressure dependence of the Debye temperature.
The comparison between experiment and first-principle and semi-empirical
calculations provide constraints on the density dependence of intermolecular
interactions in the zero-temperature limit. | cond-mat_other |
Nuclear Spin Relaxation of Very Dilute 3He impurities in Solid 4He: We report measurements of the nuclear spin-lattice and spin-spin relaxation
times of very dilute 3He in solid 4He in the temperature range 0.01 \leq T \leq
0.5 K for densities where anomalies have been observed in torsional oscillator
and shear modulus measurements. We compare the results with the values of the
relaxation times reported by other observers for higher concentrations and the
theory of Landesman that takes into account the elastic properties of the 4He
lattice. A sharp increase in the magnitude of the nuclear spin-lattice
relaxation times compared to the the classical Landesman theory is observed
close to the temperatures where the torsional and shear modulus anomalies are
observed. The NMR results suggest that the tunneling of 3He impurities in the
atomic-scale elastic distortion is affected by the same processes that give
rise to the macroscopic elastic dissipation anomalies. | cond-mat_other |
Ultrastrong coupling between a cavity resonator and the cyclotron
transition of a 2D electron gas in the case of integer filling factor: We investigate theoretically the coupling between a cavity resonator and the
cyclotron transition of a two dimensional electron gas under an applied
perpendicular magnetic field. We derive and diagonalize an effective quantum
Hamiltonian describing the magnetopolariton excitations of the two dimensional
electron gas for the case of integer filling factors. The limits of validity of
the present approach are critically discussed. The dimensionless vacuum Rabi
frequency $\Omega_0/\omega_0$ (i.e., normalized to the cyclotron frequency
$\omega_0$) is shown to scale as $\sqrt{\alpha\: n_{QW} \nu}$, where $\alpha$
is the fine structure constant, $n_{QW}$ is the number of quantum wells and
$\nu$ is the filling factor in each well. We show that with realistic
parameters of a high-mobility semiconductor two dimensional electron gas, the
dimensionless coupling $\Omega_0/\omega_0$ can be much larger than 1 in the
case of $\nu \gg 1$, the latter condition being typically realized for
cyclotron transitions in the microwave range. Implications of such ultrastrong
coupling regime are discussed. | cond-mat_other |
Dissipation-managed soliton in a quasi-one-dimensional Bose-Einstein
condensate: We use the time-dependent mean-field Gross-Pitaevskii equation to study the
formation of a dynamically-stabilized dissipation-managed bright soliton in a
quasi-one-dimensional Bose-Einstein condensate (BEC). Because of three-body
recombination of bosonic atoms to molecules, atoms are lost (dissipated) from a
BEC. Such dissipation leads to the decay of a BEC soliton. We demonstrate by a
perturbation procedure that an alimentation of atoms from an external source to
the BEC may compensate for the dissipation loss and lead to a
dynamically-stabilized soliton. The result of the analytical perturbation
method is in excellent agreement with mean-field numerics. It seems possible to
obtain such a dynamically-stabilized BEC soliton without dissipation in
laboratory. | cond-mat_other |
Influence of structure on the optical limiting properties of nanotubes: We investigate the role of carbon nanotubes structure on their optical
limiting properties. Samples of different and well-characterized structural
features are studied by optical limiting and pump-probe experiments. The
influence of the diameter's size on the nano-object is demonstrated. Indeed,
both nucleation and growth of gas bubbles are expected to be sensitive to
diameter. | cond-mat_other |
The Boron Buckyball has an Unexpected Th Symmetry: The boron buckyball avoids the high symmetry icosahedral cage structure. The
previously reported Ih symmetric structure is not an energy minimum in the
potential energy surface and exhibits a spontaneous symmetry breaking to yield
a puckered cage with a rare Th symmetry. The HOMO-LUMO gap is twice as large as
the reported value and amounts to 1.94 eV at B3LYP/6-31G(d) level. The valence
orbital structure of boron buckyball is identical to the one in the carbon
analogue. | cond-mat_other |
Proton transport and torque generation in rotary biomotors: We analyze the dynamics of rotary biomotors within a simple
nano-electromechanical model, consisting of a stator part and a ring-shaped
rotor having twelve proton-binding sites. This model is closely related to the
membrane-embedded F$_0$ motor of adenosine triphosphate (ATP) synthase, which
converts the energy of the transmembrane electrochemical gradient of protons
into mechanical motion of the rotor. It is shown that the Coulomb coupling
between the negative charge of the empty rotor site and the positive stator
charge, located near the periplasmic proton-conducting channel (proton source),
plays a dominant role in the torque-generating process. When approaching the
source outlet, the rotor site has a proton energy level higher than the energy
level of the site, located near the cytoplasmic channel (proton drain). In the
first stage of this torque-generating process, the energy of the
electrochemical potential is converted into potential energy of the
proton-binding sites on the rotor. Afterwards, the tangential component of the
Coulomb force produces a mechanical torque. We demonstrate that, at low
temperatures, the loaded motor works in the shuttling regime where the energy
of the electrochemical potential is consumed without producing any
unidirectional rotation. The motor switches to the torque-generating regime at
high temperatures, when the Brownian ratchet mechanism turns on. In the
presence of a significant external torque, created by ATP hydrolysis, the
system operates as a proton pump, which translocates protons against the
transmembrane potential gradient. Here we focus on the F$_0$ motor, even though
our analysis is applicable to the bacterial flagellar motor. | cond-mat_other |
Experimental realities refuting the existence of p=0 condensate in a
system of interacting bosons : II. Spectroscopy of embedded molecules: Experimental observation of superfluidity in a microscopic cluster,
$M:(^4He)_x$, of a molecule ($M$) and $x$ number of $^4He$ atoms (with $x$
ranging from 1 to many) is qualitatively analyzed. It concludes that: (i) each
$^4He$ atom in the cluster has to have non-zero momentum for its confinement to
a space of size ($<$ the size of the cluster), (ii) superfluidity does not
require atoms with zero momentum ($p=0$), and (iii) while all $^4He$ atoms in
the cluster cease to have relative motions (hence the inter-atomic collisions),
they retain a freedom to move coherently in order of their locations on a
closed path around the rotor ($M$ plus few nearest $^4He$ atoms which follow
the molecular rotation for their relatively strong binding with $M$). The
analysis also identifies the basic arrangement of $^4He$ atoms which allows the
rotor to have free rotation in the cluster. | cond-mat_other |
The role of interactions in spin-polarised atomic Fermi gases at
unitarity: We study the zero temperature properties of a trapped polarized Fermi gas at
unitarity by assuming phase separation between an unpolarized superfluid and a
polarized normal phase. The effects of the interaction are accounted using the
formalism of quasi-particles to build up the equation of state of the normal
phase with the Monte Carlo results for the relevant parameters. Our predictions
for the Chandrasekhar-Clogston limit of critical polarization and for the
density profiles, including the density jump at the interface, are confirmed
with excellent accuracy by the recent experimental results at MIT. The role of
interaction on the radial width of the minority component, on the gap of the RF
transition and on the spin oscillations in the normal phase is also discussed.
Our analysis points out the Fermi liquid nature of these strongly interacting
spin polarized configurations. | cond-mat_other |
Hybrid apparatus for Bose-Einstein condensation and cavity quantum
electrodynamics: Single atom detection in quantum degenerate gases: We present and characterize an experimental system in which we achieve the
integration of an ultrahigh finesse optical cavity with a Bose-Einstein
condensate (BEC). The conceptually novel design of the apparatus for the
production of BECs features nested vacuum chambers and an in-vacuo magnetic
transport configuration. It grants large scale spatial access to the BEC for
samples and probes via a modular and exchangeable "science platform". We are
able to produce \87Rb condensates of five million atoms and to output couple
continuous atom lasers. The cavity is mounted on the science platform on top of
a vibration isolation system. The optical cavity works in the strong coupling
regime of cavity quantum electrodynamics and serves as a quantum optical
detector for single atoms. This system enables us to study atom optics on a
single particle level and to further develop the field of quantum atom optics.
We describe the technological modules and the operation of the combined BEC
cavity apparatus. Its performance is characterized by single atom detection
measurements for thermal and quantum degenerate atomic beams. The atom laser
provides a fast and controllable supply of atoms coupling with the cavity mode
and allows for an efficient study of atom field interactions in the strong
coupling regime. Moreover, the high detection efficiency for quantum degenerate
atoms distinguishes the cavity as a sensitive and weakly invasive probe for
cold atomic clouds. | cond-mat_other |
Reduced Density Matrix Functional Theory at Finite Temperature:
Theoretical Foundations: We present an ab-initio approach for grand canonical ensembles in thermal
equilibrium with local or nonlocal external potentials based on the one-reduced
density matrix. We show that equilibrium properties of a grand canonical
ensemble are determined uniquely by the eq-1RDM and establish a variational
principle for the grand potential with respect to its one-reduced density
matrix. We further prove the existence of a Kohn-Sham system capable of
reproducing the one-reduced density matrix of an interacting system at finite
temperature. Utilizing this Kohn-Sham system as an unperturbed system, we
deduce a many-body approach to iteratively construct approximations to the
correlation contribution of the grand potential. | cond-mat_other |
Scaling issues for AlGaN/GaN HEMTs: performance optimization via devices
geometry modelling: The potential barrier between source and gate in HEMTs and between source and
channel in MOSFET controls the current output and the velocity injection of
electrons in the channel [1], [2]. In non self aligned structures the electric
field behavior along the channel, for fixed applied voltages, is determined by
the contacts positions. Anyway, in GaAs based HEMTs, the geometry of the device
appears to be not determinant for the output current due to saturation effects.
On the other hand, the GaN based technology still offers the possibility to
enhance devices output current handling contacts distances. In this paper we
will present Monte Carlo simulations results which show how a downscaling of
the Source to Gate distance could improve the device performances inducing an
higher potential barrier between source and gate. | cond-mat_other |
Slow-wave effect and mode-profile matching in Photonic Crystal
microcavities: Physical mechanisms involved in the light confinement in photonic crystal
slab microcavities are investigated. We first present a full three-dimensional
numerical study of these microcavities. Then, to gain physical insight into the
confinement mechanisms, we develop a Fabry-Perot model. This model provides
accurate predictions and sheds new light on the physics of light confinement.
We clearly identify two mechanisms to enhance the Q factor of these
microcavities. The first one consists in improving the mode-profile matching at
the cavity terminations and the second one in using a slow wave in the cavity. | cond-mat_other |
Scale Separation Scheme for Simulating Superfluid Turbulence:
Kelvin-Wave Cascade: A Kolmogorov-type cascade of Kelvin waves--the distortion waves on vortex
lines--plays a key part in the relaxation of superfluid turbulence at low
temperatures. We propose an efficient numeric scheme for simulating the Kelvin
wave cascade on a single vortex line. The idea is likely to be generalizable
for a full-scale simulation of different regimes of superfluid turbulence. With
the new scheme, we are able to unambiguously resolve the cascade spectrum
exponent, and thus to settle the controversy between recent simulations [1] and
recently developed analytic theory [2].
[1] W.F. Vinen, M. Tsubota and A. Mitani, Phys. Rev. Lett. 91, 135301 (2003).
[2] E.V. Kozik and B.V. Svistunov, Phys. Rev. Lett. 92, 035301 (2004). | cond-mat_other |
Equations of Two-Fluid Hydrodynamics of Superfluid Helium with the
Account of Electric Fields: System of two-fluid hydrodynamics of superfluid helium with the account of
electric field is obtained. These equations are obtained in kinetic approach
using quasi-equilibrium distribution function of quasi-particles, which vanishs
collision integral of quasi-particles, and contains dependence on electric
field by means of phenomenological parameter {\alpha}. Using experimental data
at temperature range of 1,4 - 2 K, where basic role plays roton hydrodynamics,
the value of phenomenological parameter, is obtained. | cond-mat_other |
Collective oscillations of a quasi one dimensional Bose condensate under
damping: Influence of the damping on collective oscillations of a one-dimensional
trapped Bose gas in the mean field regime has been studied. Using the
phenomenological damping approach developed by L.P. Pitaevskii, modified
variational equations for the parameters of the condensate wave function is
derived. Analytical expressions for the condensate parameters in equilibrium
state have been obtained. Bistability in nonlinear oscillations of the
condensate under periodic variations of the trap potential is predicted. The
predictions of the modified variational approach are confirmed by full
numerical simulations of the 1D GP equation with the damping. | cond-mat_other |
Comment to "Mechanism for Designing Metamaterials with a High Index of
Refraction": Comment to "Mechanism for Designing Metamaterials with a High Index of
Refraction" by J. T. Shen, Peter B. Catrysse and Shanhui Fan. | cond-mat_other |
Characterization of high-temperature PbTe p-n junctions prepared by
thermal diffusion and by ion-implantation: We describe here the characteristics of two types of high-quality PbTe
p-n-junctions, prepared in this work: (1) by thermal diffusion of In4Te3 gas
(TDJ), and (2) by ion implantation (implanted junction, IJ) of In (In-IJ) and
Zn (Zn-IJ). The results, as presented here, demonstrate the high quality of
these PbTe diodes. Capacitance-voltage and current-voltage characteristics have
been measured. The measurements were carried out over a temperature range from
~ 10 K to ~ 180 K. The latter was the highest temperature, where the diode
still demonstrated rectifying properties. This maximum operating temperature is
higher than any of the earlier reported results.
The saturation current density, J0, in both diode types, was ~ 10^-5 A/cm2 at
80 K, while at 180 K J0 ~ 10^-1 A/cm2 in TDJ and ~ 1 A/cm2 in both
ion-implanted junctions. At 80 K the reverse current started to increase
markedly at a bias of ~ 400 mV for TDJ, and at ~550 mV for IJ. The ideality
factor n was about 1.5-2 for both diode types at 80 K. The analysis of the C-V
plots shows that the junctions in both diode types are linearly graded. The
analysis of the C-V plots allows also determining the height of the junction
barrier, the concentrations and the concentration gradient of the impurities,
and the temperature dependence of the static dielectric constant. The
zero-bias-resistance x area products (R0Ae) at 80 K are: 850 OHMcm2 for TDJ,
250 OHMcm2 for In-IJ, and ~ 80 OHMcm2 for Zn-IJ, while at 180 K R0Ae ~ 0.38
OHMcm2 for TDJ, and ~ 0.1 OHMcm2 for IJ. The estimated detectivity is: D* ~
10^10 cmHz^(1/2)/W up to T=140 K, determined mainly by background radiation,
while at T=180 K, D* decreases to 108-107 cmHz^(1/2)/W, and is determined by
the Johnson noise. | cond-mat_other |
Evidence for Efimov quantum states in an ultracold gas of cesium atoms: Systems of three interacting particles are notorious for their complex
physical behavior. A landmark theoretical result in few-body quantum physics is
Efimov's prediction of a universal set of bound trimer states appearing for
three identical bosons with a resonant two-body interaction.
Counterintuitively, these states even exist in the absence of a corresponding
two-body bound state. Since the formulation of Efimov's problem in the context
of nuclear physics 35 years ago, it has attracted great interest in many areas
of physics. However, the observation of Efimov quantum states has remained an
elusive goal. Here we report the observation of an Efimov resonance in an
ultracold gas of cesium atoms. The resonance occurs in the range of large
negative two-body scattering lengths, arising from the coupling of three free
atoms to an Efimov trimer. Experimentally, we observe its signature as a giant
three-body recombination loss when the strength of the two-body interaction is
varied. We also detect a minimum in the recombination loss for positive
scattering lengths, indicating destructive interference of decay pathways. Our
results confirm central theoretical predictions of Efimov physics and represent
a starting point with which to explore the universal properties of resonantly
interacting few-body systems. While Feshbach resonances have provided the key
to control quantum-mechanical interactions on the two-body level, Efimov
resonances connect ultracold matter to the world of few-body quantum phenomena. | cond-mat_other |
Quantum Turbulence of Bellows-Driven 4He Superflow: Decay: We report on studies of quantum turbulence with second-sound in superfluid
4He in which the turbulence is generated by the flow of the superfluid
component through a wide square channel, the ends of which are plugged with
sintered silver superleaks, the flow being generated by compression of a
bellows. The superleaks ensure that there is no net flow of the normal fluid.
In an earlier paper (Phys. Rev. B, 86, 134515 (2012)) we have shown that steady
flow of this kind generates a density of vortex lines that is essentially
identical with that generated by thermal counterflow, when the average relative
velocity between the two fluids is the same. In this paper we report on studies
of the temporal decay of the vortex-line density, observed when the bellows is
stopped, and we compare the results with those obtained from the temporal decay
of thermal counterflow re-measured in the same channel and under the same
conditions. In both cases here is an initial fast decay which, for low enough
initial line density approaches for a short time the form $t^{-1}$
characteristic of the decay of a random vortex tangle. This is followed at late
times by a slower $t^{-3/2}$ decay, characteristic of the decay of large
'quasi-classical eddies'. However, in the range of investigated parameters, we
observe always in the case of thermal counterflow, and only in a few cases of
high steady-state velocity in superflow, an intermediate regime in which the
decay either does not proceed monotonically with time or passes through a point
of inflexion. This difference, established firmly by our experiments, might
represent one essential ingredient for the full theoretical understanding of
counterflow turbulence. | cond-mat_other |
New Heat-Capacity Measurements of the Possible Order-Disorder Transition
in the 4/7-phase of 2D Helium: We have developed a new heat-capacity measuring system with ZYX graphite that
is known to have much better crystallinity than Grafoil and started data
collection. We report preliminary data as well as a detailed description of
instrumentation including a mechanical heat-switch operated by hydraulic
pressure of superfluid helium-4. | cond-mat_other |
Non-perturbative embedding of local defects in crystalline materials: We present a new variational model for computing the electronic first-order
density matrix of a crystalline material in presence of a local defect. A
natural way to obtain variational discretizations of this model is to expand
the difference Q between the density matrix of the defective crystal and the
density matrix of the perfect crystal, in a basis of precomputed maximally
localized Wannier functions of the reference perfect crystal. This approach can
be used within any semi-empirical or Density Functional Theory framework. | cond-mat_other |
Formation of a condensed state with macroscopic number of phonons in
ultracold Bose gases: A mechanism for the formation of a new type of stationary state with
macroscopical number of phonons in condensed atomic gases is proposed. This
mechanism is based on generating longitudinal phonons as a result of parametric
resonance caused by a permanent modulation of the transverse trap frequency in
an elongated trap. The phonon-phonon interaction predetermines the
self-consistent evolution which is completed with macroscopic population of one
from all levels within the energy interval of parametric amplification. This
level proves to be shifted to the edge of this interval. All other levels end
the evolution with zero population. | cond-mat_other |
Exponentially Fragile PT-Symmetry in Lattices with Localized Eigenmodes: We study the effect of localized modes in lattices of size N with parity-time
(PT) symmetry. Such modes are arranged in pairs of quasi-degenerate levels with
splitting delta exp{-N/xi}, where \xi is their localization length. The level
"evolution" with respect to the PT breaking parameter gamma shows a cascade of
bifurcations during which a pair of real levels becomes complex. The
spontaneous PT symmetry breaking occurs at gamma min(delta), thus resulting in
an exponentially narrow exact PT phase. As N/xi decreases, it becomes more
robust with gamma (1/N)^2 and the distribution P(gamma) changes from log-normal
to semi-Gaussian. Our theory can be tested in the frame of optical lattices. | cond-mat_other |
Three-body Recombination of Lithium-6 Atoms with Large Negative
Scattering Lengths: The 3-body recombination rate at threshold for distinguishable atoms with
large negative pair scattering lengths is calculated in the zero-range
approximation. The only parameters in this limit are the 3 scattering lengths
and the Efimov parameter, which can be complex valued. We provide semi-analytic
expressions for the cases of 2 or 3 equal scattering lengths and we obtain
numerical results for the general case of 3 different scattering lengths. Our
general result is applied to the three lowest hyperfine states of Lithium-6
atoms. Comparisons with recent experiments provide indications of loss features
associated with Efimov trimers near the 3-atom threshold. | cond-mat_other |
Spin dynamics of a trapped spin-1 Bose Gas above the Bose-Einstein
transition temperature: We study collective spin oscillations in a spin-1 Bose gas above the
Bose-Einstein transition temperature. Starting from the Heisenberg equation of
motion, we derive a kinetic equation describing the dynamics of a thermal gas
with the spin-1 degree of freedom. Applying the moment method to the kinetic
equation, we study spin-wave collective modes with dipole symmetry. The dipole
modes in the spin-1 system are found to be classified into the three type of
modes. The frequency and damping rate are obtained as functions of the peak
density. The damping rate is characterized by three relaxation times associated
with collisions. | cond-mat_other |
Lindemann Criterion and the Anomalous Melting Curve of Sodium: Recent reports of the melting curve of sodium at high pressure have shown
that it has a very steep descent after a maximum of around 1000K at 31 GPa.
This is not due to a phase transition. According to the Lindemann criterion,
this behaviour should be apparent in the evolution of the Debye temperature
with pressure. In this work, we have performed an "ab-initio" analysis of the
behaviour of both the Debye temperature and the elastic constants up to 102
GPa, and find a clear trend at high pressure that should cause a noticeable
effect on the melting curve. | cond-mat_other |
Parametric spin excitations in lateral quantum dots: In this work, the spin dynamics of a single electron under parametric
modulation of a lateral quantum dot's electrostatic potential in the presence
of spin-orbit coupling is investigated. Numerical and theoretical calculations
demonstrate that, by squeezing and/or moving the electron's wave function, spin
rotations with Rabi frequencies on the order of tens of megahertz can be
achieved with experimentally accessible parameters in both parabolic and square
lateral quantum dots. Applications of parametric excitations for determining
spin-orbit coupling parameters and for increasing the spin polarization in the
electronic ground are demonstrated. | cond-mat_other |
Exact Study of the 1D Boson Hubbard Model with a Superlattice Potential: We use Quantum Monte Carlo simulations and exact diagonalization to explore
the phase diagram of the Bose-Hubbard model with an additional superlattice
potential. We first analyze the properties of superfluid and insulating phases
present in the hard-core limit where an exact analytic treatment is possible
via the Jordan-Wigner transformation. The extension to finite on-site
interaction is achieved by means of quantum Monte Carlo simulations. We
determine insulator/superfluid phase diagrams as functions of the on-site
repulsive interaction, superlattice potential strength, and filling, finding
that insulators with fractional occupation numbers, which are present in the
hard-core case, extend deep into the soft-core region. Furthermore, at integer
fillings, we find that the competition between the on-site repulsion and the
superlattice potential can produce a phase transition between a Mott insulator
and a charge density wave insulator, with an intermediate superfluid phase. Our
results are relevant to the behavior of ultracold atoms in optical
superlattices which are beginning to be studied experimentally. | cond-mat_other |
Experimental study of the transport of coherent interacting matter-waves
in a 1D random potential induced by laser speckle: We present a detailed analysis of the 1D expansion of a coherent interacting
matterwave (a Bose-Einstein condensate) in the presence of disorder. A 1D
random potential is created via laser speckle patterns. It is carefully
calibrated and the self-averaging properties of our experimental system are
discussed. We observe the suppression of the transport of the BEC in the random
potential. We discuss the scenario of disorder-induced trapping taking into
account the radial extension in our experimental 3D BEC and we compare our
experimental results with the theoretical predictions. | cond-mat_other |
Topological quantum correction to an atomic ideal gas law as a dark
energy effect: The traditional ambiguity about the bulk electrostatic potentials in crystals
is due to the conditional convergence of Coulomb series. The classical Ewald
approach turns out to be the first one resolving this task as consistent with a
translational symmetry. The latter result appears to be directly associated
with the thermodynamic limit in crystals. In this case the solution can also be
obtained upon direct lattice summation, but after subtracting the mean Bethe
potential. As shown, this effect is associated with special periodic boundary
conditions at infinity so as to neutralize an arbitrary choice of the unit-cell
charge distribution. However, the fact that any additional potential exerted by
some charge distribution must in turn affect that charge distribution in
equilibrium is not discussed in the case at hand so far. Here we show that in
the simplest event of gaseous atomic hydrogen as an example, the
self-consistent mean-field-potential correction results in an additional
pressure contribution to an ideal gas law. As a result, the corresponding
correction to the sound velocity arises. Moreover, if gas in question is not
bounded by any fixed volume, then some acceleration within that medium is
expected. Addressed to the Friedman hypersphere, our result may be interesting
in connection with the accelerating Universe revealed experimentally and
discussed intensively. | cond-mat_other |
Vortex Properties of a Resonant Superfluid: The properties of a vortex in a rotating superfluid Fermi gas are studied in
the unitary limit. A phenomenological approach based on Ginzburg-Landau theory
is developed for this purpose. The density profiles, including those of the
normal fluid and superfluid, are obtained at various temperatures and rotation
frequencies. The superfluid and normal fluid densities can be identified from
the angular momentum density. The total free energy and angular momentum of the
vortex are also obtained. | cond-mat_other |
Dynamics of rapidly rotating Bose-Einstein condensates in a harmonic
plus quartic trap: A two-dimensional rapidly rotating Bose-Einstein condensate in a harmonic
plus quartic trap is expected to have unusual vortex states that do not occur
in a pure harmonic trap. At a critical rotation speed $\Omega_h$, a central
hole appears in the condensate, and at some faster rotation speed $\Omega_g$,
the system undergoes a transition to a giant vortex state with pure
irrotational flow. Using a time-dependent variational analysis, we study the
behavior of an annular condensate with a single concentric ring of vortices.
The transition to a giant vortex state is investigated by comparing the energy
of the two equilibrium states (the ring of vortices and the giant vortex) and
also by studying the dynamical stability of small excitation modes of the ring
of vortices. | cond-mat_other |
Exactly solvable model of electron in the Lame potential and
singularities of the electron thermodynamic potential: One-gap and two-gap separable Lame potentials are studied in detail. For the
one-dimensional case, we construct the dispersion relation graph E(k) and for
the three-dimensional case we construct the Fermi surfaces in the first and
second bands. The pictures illustrate a passage from the limit case of free
electrons to the limit case of tight binding electrons. These results are used
to describe the Lifshits electron phase transition of 2.5 kind and derive some
exact expressions. We also examine the singularities of the second derivative
of magnetic momentum in an external magnetic field. The parameter of the
singularities depends on corresponding effective mass. | cond-mat_other |
Half-vortices in polariton condensates: It is shown that vortices in linearly polarized polariton condensates in
planar semiconductor microcavities carry two winding numbers (k,m). These
numbers can be either integer or half-integer simultaneously. Four half-integer
vortices (1/2,1/2), (-1/2,-1/2), (1/2,-1/2), and (-1/2,1/2) are anisotropic,
possess the smallest energy, and define the Kosterlitz-Thouless transition
temperature. The condensate concentration remains finite within the core of
half-vortex and the polarization becomes fully circular in the core center. | cond-mat_other |
Influence of an external magnetic field on the decoherence of a central
spin coupled to an antiferromagnetic environment: Using the spin wave approximation, we study the decoherence dynamics of a
central spin coupled to an antiferromagnetic environment under the application
of an external global magnetic field. The external magnetic field affects the
decoherence process through its effect on the antiferromagnetic environment. It
is shown explicitly that the decoherence factor which displays a Gaussian decay
with time depends on the strength of the external magnetic field and the
crystal anisotropy field in the antiferromagnetic environment. When the values
of the external magnetic field is increased to the critical field point at
which the spin-flop transition (a first-order quantum phase transition) happens
in the antiferromagnetic environment, the decoherence of the central spin
reaches its highest point. This result is consistent with several recent
quantum phase transition witness studies. The influences of the environmental
temperature on the decoherence behavior of the central spin are also
investigated. | cond-mat_other |
Vortex-line solitons in a periodically modulated Bose gas: We study the nonlinear excitations of a vortex-line in a Bose-Einstein
condensate trapped in a one-dimensional optical lattice. We find that the
classical Euler dynamics of the vortex results in a description of the vortex
line in terms of a (discrete) one-dimensional Gross-Pitaevskii equation, which
allows for both bright and gray soliton solutions. We discuss these solutions
in detail and predict that it is possible to create vortex-line solitons with
current experimental capabilities. | cond-mat_other |
Neutron Reflection from the Surface of Liquid 4He with and without a
Layer of 3He: We report and discuss the first neutron reflection measurements from the free
surface of normal and superfluid 4He and of liquid 3He-4He mixture. In case of
liquid 4He the surface roughness is different above and below the lambda
transition, being smoother in the superfluid state. For the superfluid, we also
observe the formation of a surface layer ~200 A thick which has a subtly
different neutron scattering cross-section. The results can be interpreted as
an enhancement of Bose-Einstein condensate fraction close to the helium
surface. We find that the addition of 3He isotopic impurities leads to the
formation of Andreev levels at low temperatures. | cond-mat_other |
Spin Collective Modes of Two-Species Fermi Liquids: Helium-3 and Atomic
Gases near the Feshbach Resonance: We present theoretical findings on the spin collective modes of a two-species
Fermi liquid, prepared alternatively in a polarized equilibrium or a polarized
non-equilibrium state. We explore the effects on these modes of a diverging
s-wave scattering length, as occurs near a Feshbach resonance in a Fermionic
atomic gas. We compare these atomic gas modes with those of the conventional
Helium-3 system, and we find that they differ from the conventional systems,
and that the gap and spin stiffness are tunable via the Feshbach resonance. | cond-mat_other |
Statistical Facts of Artificial Stock Market: The paper reports the construction of artificial stock market that emerges
the similar statistical facts with real data in Indonesian stock market. We use
the individual but dominant data, i.e.: PT TELKOM in hourly interval. The
artificial stock market shows standard statistical facts, e.g.: volatility
clustering, the excess kurtosis of the distribution of return, and the scaling
properties with its breakdown in the crossover of Levy distribution to the
Gaussian one. From this point, the artificial stock market will always be
evaluated in order to have comprehension about market process in Indonesian
stock market generally. | cond-mat_other |
The role of the coherence in the cross-correlation analysis of
diffraction patterns from two-dimensional dense mono-disperse systems: The investigation of the static and dynamic structural properties of
colloidal systems relies on techniques capable of atomic resolution in real
space and femtosecond resolution in time. Recently, the cross-correlation
function (CCF) analysis of both X-rays and electron diffraction patterns from
dilute and dense aggregates has demonstrated the ability to retrieve
information on the sample's local order and symmetry. Open questions remain
regarding the role of the beam coherence in the formation of the diffraction
pattern and the properties of the CCF, especially in dense systems. Here, we
simulate the diffraction patterns of dense two-dimensional monodisperse systems
of different symmetries, varying the transverse coherence of the probing wave,
and analyze their CCF. We study samples with different symmetries at different
size scale, as for example, pentamers arranged into a four-fold lattice where
each pentamer is surrounded by triangular lattices, both ordered and
disordered. In such systems, different symmetry modulations are arising in the
CCF at specific scattering vectors. We demonstrate that the amplitude of the
CCF is a fingerprint of the degree of the ordering in the sample and that at
partial transverse coherence, the CCF of a dense sample corresponds to that of
an individual scattering object. | cond-mat_other |
Quantized vortices in atomic Bose-Einstein condensates: In this review, we give an overview of the experimental and theoretical
advances in the physics of quantized vortices in dilute atomic-gas
Bose--Einstein condensates in a trapping potential, especially focusing on
experimental research activities and their theoretical interpretations. Making
good use of the atom optical technique, the experiments have revealed many
novel structural and dynamic properties of quantized vortices by directly
visualizing vortex cores from an image of the density profiles. These results
lead to a deep understanding of superfluid hydrodynamics of such systems.
Typically, vortices are stabilized by a rotating potential created by a laser
beam, magnetic field, and thermal gas. Finite size effects and inhomogeneity of
the system, originating from the confinement by the trapping potential, yield
unique vortex dynamics coupled with the collective excitations of the
condensate. Measuring the frequencies of the collective modes is an accurate
tool for clarifying the character of the vortex state. The topics included in
this review are the mechanism of vortex formation, equilibrium properties, and
dynamics of a single vortex and those of a vortex lattice in a rapidly rotating
condensate. | cond-mat_other |
Simulations of financial markets in a Potts-like model: A three-state model based on the Potts model is proposed to simulate
financial markets. The three states are assigned to "buy", "sell" and
"inactive" states. The model shows the main stylized facts observed in the
financial market: fat-tailed distributions of returns and long time
correlations in the absolute returns. At low inactivity rate, the model
effectively reduces to the two-state model of Bornholdt and shows similar
results to the Bornholdt model. As the inactivity increases, we observe the
exponential distributions of returns. | cond-mat_other |
Low-Temperature Mobility of Surface Electrons and Ripplon-Phonon
Interaction in Liquid Helium: The low-temperature dc mobility of the two-dimensional electron system
localized above the surface of superfluid helium is determined by the slowest
stage of the longitudinal momentum transfer to the bulk liquid, namely, by the
interaction of surface and volume excitations of liquid helium, which rapidly
decreases with temperature. Thus, the temperature dependence of the
low-frequency mobility is \mu_{dc} = 8.4x10^{-11}n_e T^{-20/3} cm^4 K^{20/3}/(V
s), where n_e is the surface electron density. The relation
T^{20/3}E_\perp^{-3} << 2x10^{-7} between the pressing electric field (in
kV/cm) and temperature (in K) and the value \omega < 10^8 T^5 K^{-5}s^{-1} of
the driving-field frequency have been obtained, at which the above effect can
be observed. In particular, E_\perp = 1 kV/cm corresponds to T < 70 mK and
\omega/2\pi < 30 Hz. | cond-mat_other |
Binding Energies of 6Li p-wave Feshbach Molecules: We present measurements of the binding energies of $^6$Li p-wave Feshbach
molecules formed in combinations of the (F = 1/2, m_F = +1/2), (1), and (F =
1/2, m_F = -1/2), (2), states. The binding energies scale linearly with
magnetic field detuning for all three resonances. The relative molecular
magnetic moments are found to be $113 \pm 7 \mu$K/G, $111 \pm 6 \mu$K/G and
$118 \pm 8 \mu$K/G for the (1)-(1), (1)-(2) and (2)-(2) resonances,
respectively, in good agreement with theoretical predictions. Closed channel
amplitudes and the size of the p-wave molecules are obtained theoretically from
full closed-coupled calculations. | cond-mat_other |
Rotating states for trapped bosons in an optical lattice: Rotational states for trapped bosons in an optical lattice are studied in the
framework of the Hubbard model. Critical frequencies are calculated and the
main parameter regimes are identified. Transitions are observed from edge
superfluids to vortex lattices with Mott insulating cores, and subsequently to
lattices of interstitial vortices. The former transition coincides with the
Mott transition. Changes in symmetry of the vortex lattices are observed as a
function of lattice depth. Predictions for experimental signatures are
presented. | cond-mat_other |
Two objective and independent fracture parameters for interface cracks
and a paradox: Due to the oscillatory singular stress field around a crack tip, interface
fracture has some peculiar features. This paper is focused on two of them. One
can be reflected by a proposed paradox that geometrically similar structures
with interface cracks under similar loadings may have different failure
behaviors. The other one is that the existing fracture parameters of the
oscillatory singular stress field, such as a complex stress intensity factor,
exhibit some non-objectivity because their phase angle depend on an arbitrarily
chosen length. Two objective and independent fracture parameters are proposed
which can fully characterize the stress field near the crack tip. One parameter
represents the stress intensity with classical unit of stress intensity
factors. It is interesting to find that the loading mode can be characterized
by a length as the other parameter, which can properly reflect the phase of the
stress oscillation with respect to the distance to the crack tip. This is quite
different from other crack tip fields in which the loading mode is usually
expressed by a phase angle. The corresponding failure criterion for interface
cracks does not include any arbitrarily chosen quantity, and therefore is
convenient for comparing and accumulating experimental results, even existing
ones. | cond-mat_other |
Condon domains - these non-magnetic diamagnetic domains: The paper, not pretending for a complete and detailed review, is intended
mainly for a wide community of physicists, not only specialists in this
particular subject. The author gives a physical picture of the periodic
emergence of instabilities and well-known diamagnetic domains (Condon domains)
in metals resulting from the strong de Haas-van Alphen effect. The most
significant experiments on observation and study of the domain state in metals
are described. In particular, the recent achievements in this area using muon
spin rotation, as well as the amazing phenomenon of "supersoftness" observed in
the magnetostriction experiments, are presented. Novel, not previously
discussed features of the phenomenon related to the metal compressibility are
enlightened. | cond-mat_other |
La-dilution effects in TbRhIn5 antiferromagnet: We report measurements of temperature dependent magnetic susceptibility,
resonant x-ray magnetic scattering (XRMS) and heat capacity on single crystals
of Tb1-xLaxRhIn5 for nominal concentrations in the range 0.0 < x < 1.0. TbRhIn5
is an antiferromagnetic (AFM) compound with TN ~ 46 K, which is the highest TN
values along the RRhIn5 series. We explore the suppression of the
antiferromagnetic (AFM) state as a function of La-doping considering the
effects of La-induced dilution and perturbations to the tetragonal crystalline
electrical field (CEF) on the long range magnetic interaction between the
Tb$^{3+}$ ions. Additionally, we also discuss the role of disorder. Our results
and analysis are compared to the properties of the undoped compound and of
other members of the RRhIn5 family and structurally related compounds (R2RhIn8
and RIn3). The XRMS measurements reveal that the commensurate magnetic
structure with the magnetic wave-vector (0,1/2,1/2) observed for the undoped
compound is robust against doping perturbations in Tb0.6La0.4RhIn5 compound. | cond-mat_other |
Magnetism and structure of magnetic multilayers based on the fully spin
polarized Heusler alloys Co2MnGe and Co2MnSn: Our Introduction starts with a short general review of the magnetic and
structural properties of the Heusler compounds which are under discussion in
this book. Then, more specifically, we come to the discussion of our
experimental results on multilayers composed of the Heusler alloys Co2MnGe and
Co2MnSn with V or Au as interlayers. The experimental methods we apply combine
magnetization and magneto-resistivity measurements, x-ray diffraction and
reflectivity, soft x-ray magnetic circular dichroism and spin polarized neutron
reflectivity. We find that below a critical thickness of the Heusler layers at
typically dcr = 1.5 nm the ferromagnetic order is lost and spin glass order
occurs instead. For very thin ferromagnetic Heusler layers there are
peculiarities in the magnetic order which are unusual when compared to
conventional ferromagnetic transition metal multilayer systems. In [Co2MnGe/Au]
multilayers there is an exchange bias shift at the ferromagnetic hysteresis
loops at low temperatures caused by spin glass ordering at the interface. In
[Co2MnGe/V] multilayers we observe an antiferromagnetic interlayer long range
ordering below a well defined Neel temperature originating from the dipolar
stray fields at the magnetically rough Heusler layer interfaces. | cond-mat_other |
Anomalous reflection and excitation of surface waves in metamaterials: We consider reflection of electromagnetic waves from layered structures with
various dielectric and magnetic properties, including metamaterials. Assuming
periodic variations in the permittivity, we find that the reflection is in
general anomalous. In particular, we note that the specular reflection vanishes
and that the incident energy is totally reflected in the backward direction,
when the conditions for resonant excitation of leaking surface waves are
fulfilled. | cond-mat_other |
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