pinecone/core-2020-05-10-deduplication huggingface dataset:
Ultracold atom superfluidity induced by the Feshbach resonance

We discuss the possible signatures of superfluidity induced by the Feshbach
resonance in ultracold gas of fermion atoms. Approaching the phase transition
from above there appear various manifestations of the gradually emerging order
parameter, but yet the long range coherence is not established due to strong
quantum fluctuations. The single particle excitation spectrum becomes gapped
while at the same time the pair excitations are characterized by the narrow
quasiparticle peak surrounded by the incoherent background. This quasiparticle
shows up certain collective features such as the remnant of the "first sound"
which at Tc spreads down to low momenta. Presence of this Goldstone mode is the
most unambiguous proof for appearance of the superfluid state. We discuss how
such mode can be detected experimentally.Comment: 5 pages, 3 figure
High-Tc Cuprate Superconductivity in a Nutshell

Since the discovery of high-Tc cuprate superconductivity in 1986 many new
experimental techniques and theoretical concepts have been developed. In
particular it was shown that the BCS theory of d-wave superconductivity
describes semi-quantitatively the high-Tc superconductivity. Furthermore, it
was demonstrated that Volovik's approach is extremely useful for finding the
quasiparticle properties in the vortex state. Here we survey these developments
and forecast future directions.Comment: 11 pages, 3 figure
Interplay of orbitally polarized and magnetically ordered phases in
  doped transition metal oxides

We investigate the magnetic instabilities of the two-dimensional model of
interacting e_g electrons for hole doping away from two electrons per site in
the mean-field approximation. In particular, we address the occurrence of
orbitally polarized states due to the inequivalent orbitals, and their
interplay with ferromagnetic and antiferromagnetic spin order. The role played
by the Hund's exchange coupling J_H and by the crystal field orbital splitting
E_z in stabilizing one of the competing phases is discussed in detail.Comment: 7 pages, 4 figure
Onset of metallic ferromagnetism in a doped spin-orbital chain

Starting from a spin-orbital model for doped manganites, we investigate a
competition between ferromagnetic and antiferromagnetic order in a
one-dimensional model at finite temperature. The magnetic and orbital order at
half filling support each other and depend on a small antiferromagnetic
superexchange between t_{2g} spins and on an alternating Jahn-Teller potential.
The crossover to a metallic ferromagnetic phase found at finite doping is
partly suppressed by the Jahn-Teller potential which may localize e_g
electrons.Comment: 6 pages, 4 figures, contribution to ICTP Ustron, 2004, see phys.
  stat. sol. at http://www.interscience.wiley.co
Scanning tunneling microscopy of monoatomic gold chains on vicinal
  Si(335) surface: experimental and theoretical study

We study electronic and topographic properties of the Si(335) surface,
containing Au wires parallel to the steps. We use scanning tunneling microscopy
(STM) supplemented by reflection of high energy electron diffraction (RHEED)
technique. The STM data show the space and voltage dependent oscillations of
the distance between STM tip and the surface which can be explained within one
band tight binding Hubbard model. We calculate the STM current using
nonequilibrium Keldysh Green function formalism.Comment: 6 pages, 4 figure
'Pi State' Induced by Impurities with a Repulsive Interaction

We study the properties of a quantum impurity embedded in a superconducting
host. The superconductor is described by the negative U Hubbard model while the
impurity introduces a repulsive interaction to the system. We discuss the
influence of this `on-impurity' Coulomb repulsion on the local properties
(density of states, electron pairing) of the superconductor. We show the
condition of pi - like behaviour, defined as two subsystems having a phase
difference of pi, in the system by using a proper combination of attractive
pairing interaction and repulsive one located at impurity site.Comment: 5 pages, 4 figures, to be published in Physica Status Solidi
Rough surface scattering in many-mode conducting channels: Gradient
  versus amplitude scattering

We study the effect of surface scattering on transport properties in
many-mode conducting channels (electron waveguides). Assuming a strong
roughness of the surface profiles, we show that there are two independent
control parameters that determine statistical properties of the scattering. The
first parameter is the ratio of the amplitude of the roughness to the
transverse width of the waveguide. The second one, which is typically omitted,
is determined by the mean value of the derivative of the profile. This
parameter may be large, thus leading to specific properties of scattering. Our
results may be used in experimental realizations of the surface scattering of
electron waves, as well as for other applications (e.g., for optical and
microwave waveguides)Comment: 6 pages, no figure
AC-Stark effect in a semi-spherical quantum dot

We present a theoretical approach to study the effects of an ac-field applied
to quantum dots with semi-spherical symmetry. Using the Floquet formalism for
this periodically driven system, the time-dependent Hamiltonian in the
effective mass approximation is solved. We show that the Hilbert space of
solutions is separated into orthogonal subspaces with different $z$-component
of the angular momentum. We give an explicit analytical representation for
electronic states as a function of the intensity and frequency of the electric
field. Under the two level approximation, two particular cases are studied: the
low- and high-frequency regimes, which result of comparing the ac-field
frequency to the characteristic level splitting at zero field.Comment: 3 pages, one figur
On Dislocations in a Special Class of Generalized Elasticity

In this paper we consider and compare special classes of static theories of
gradient elasticity, nonlocal elasticity, gradient micropolar elasticity and
nonlocal micropolar elasticity with only one gradient coefficient. Equilibrium
equations are discussed. The relationship between the gradient theory and the
nonlocal theory is discussed for elasticity as well as for micropolar
elasticity. Nonsingular solutions for the elastic fields of screw and edge
dislocations are given. Both the elastic deformation (distortion, strain,
bend-twist) and the force and couple stress tensors do not possess any
singularity unlike `classical' theories.Comment: 28 pages, to appear in: physica status solid
Thermodynamic origin of order parameters in mean-field models of spin
  glasses

We analyze thermodynamic behavior of general $n$-component mean-field spin
glass models in order to identify origin of the hierarchical structure of the
order parameters from the replica-symmetry breaking solution. We derive a
configurationally dependent free energy with local magnetizations and averaged
local susceptibilities as order parameters. On an example of the replicated
Ising spin glass we demonstrate that the hierarchy of order parameters in
mean-field models results from the structure of inter-replica susceptibilities.
These susceptibilities serve for lifting the degeneracy due to the existence of
many metastable states and for recovering thermodynamic homogeneity of the free
energy.Comment: REVTeX4, 13 pages, 8 EPS figure
Structural distortions of frustrated quantum spin lattices in high
  magnetic fields

We study the stability of some strongly frustrated antiferromagnetic spin
lattices in high magnetic fields against lattice distortions. In particular, we
consider a spin-s anisotropic Heisenberg antiferromagnet on the
square-kagom\'{e} and kagom\'{e} lattices. The independent localized magnons
embedded in a ferromagnetic environment, which are the ground state at the
saturation field, imply lattice instabilities for appropriate lattice
distortions fitting to the structure of the localized magnons. We discuss in
detail the scenario of this spin-Peierls instability in high magnetic fields
which essentially depends on the values of the exchange interaction anisotropy
\Delta and spin s
Interface disorder and layer transitions in Ising thin films

The disorder and layer transitions in the interface between an Ising spin-1/2
film denoted $(n)$, and an Ising spin-1 film denoted $(m)$, are studied using
Monte Carlo simulations. The effects of both an external magnetic field, acting
only on the spin-1/2 film, and a crystal magnetic field acting only on the
spin-1 film, are studied for a fixed temperature and selected values of the
coupling constant $J_p$ between the two films. It is found that for large
values of the constant $J_p$, the layers of the film $(n)$, as well as those of
the film $(m)$, undergo a first order layering transition. On the other hand,
the only disordered layer of the film $(n)$ is that one belonging to the
interface films $(n)/(m)$, for any values of the crystal field $\Delta$. We
show the existence of a critical value of the crystal field $\Delta_c$, above
which this particular layer of the film $(n)$ is disordered. We found that
$\Delta_c$ depends on the values of the constant coupling $(J_p)$ between the
two films.Comment: 6 pages Latex, 13 figures Postscript forma
Magnetic plateaus in the 1D antiferromagnetic spin-3/2 and spin-2 Ising
  chains with single-ion anisotropy

In this study, we have employed the classical transfer matrix technique to
investigate the magnetization plateaus, phase diagrams and other
thermodynamical properties of the one-dimensional antiferromagnetic spin-3/2
and spin-2 Ising chains with single-ion anisotropy in the presence of an
external magnetic field at very low temperature. We have showed that single
ion-anisotropy is one of the indispensable ingredients for an energy gap which
leads to magnetic plateau mechanism in one-dimensional antiferromagnetic Ising
spin chains. Other thermodynamical predictions seem to be provide this
argument.Comment: 14 pages, 15 Figure
Correlation effects in the valence bands of ferromagnetic semiconductor
  EuS

We present a many body analysis of the multi-band Kondo lattice model. The
study is then combined with the first principles TB-LMTO band structure
calculations, in order to investigate the temperature dependent correlation
effects in the 3$\textit{p}$ valence bands of the ferromagnetic semiconductor
EuS. Some of the physical properties of interest like the quasi-particle
density of states (Q-DOS), spectral density (SD) and quasi-particle band
structure (Q-BS) are calculated and discussed. Therewith, we propose a spin
resolved ARPES of the valence bands of EuS to be performed.Comment: 12 pages, 10 figures, accepted for publication in Phys. Stat. Solidi
Weak universality, bicritical points and reentrant transitions in the
  critical behaviour of a mixed spin-1/2 and spin-3/2 Ising model on the union
  jack (centered square) lattice

The mixed spin-1/2 and spin-3/2 Ising model on the union jack lattice is
solved by establishing a mapping correspondence with the eight-vertex model. It
is shown that the model under investigation becomes exactly soluble as a
free-fermion eight-vertex model when the parameter of uniaxial single-ion
anisotropy tends to infinity. Under this restriction, the critical points are
characterized by critical exponents from the standard Ising universality class.
In a certain subspace of interaction parameters, which corresponds to a
coexistence surface between two ordered phases, the model becomes exactly
soluble as a symmetric zero-field eight-vertex model. This surface is bounded
by a line of bicritical points having interaction-dependent critical exponents
that satisfy a weak universality hypothesis.Comment: 8 pages, 8 figure
Three real-space discretization techniques in electronic structure
  calculations

A characteristic feature of the state-of-the-art of real-space methods in
electronic structure calculations is the diversity of the techniques used in
the discretization of the relevant partial differential equations. In this
context, the main approaches include finite-difference methods, various types
of finite-elements and wavelets. This paper reports on the results of several
code development projects that approach problems related to the electronic
structure using these three different discretization methods. We review the
ideas behind these methods, give examples of their applications, and discuss
their similarities and differences.Comment: 39 pages, 10 figures, accepted to a special issue of "physica status
  solidi (b) - basic solid state physics" devoted to the CECAM workshop "State
  of the art developments and perspectives of real-space electronic structure
  techniques in condensed matter and molecular physics". v2: Minor stylistic
  and typographical changes, partly inspired by referee comment
Some electronic and optical properties of self-assembled quantum dots:
  asymmetries in a lens domain

The self-assembled quantum dot with lens domain has rotational symmetry but
it is intrinsically asymmetric when the electron moves perpendicularly to its
circular base, {\it i. e.} along the rotational axis. To characterize this
asymmetry, an external electric field is applied along the positive or negative
direction of the rotational axis. We report the different Stark shifts
appearing in the spectra as a function of the field intensity for different
lens domains. It is shown that for a flat lens domain the asymmetry effects
decrease, but even for very flat lenses they can not be approximated by a
cylindrical domain. Finally, some optical properties such as the dielectric
constant and electroabsorption are studied. Signatures of the energy spectrum
reveal in these quantities. The importance of considering the proper lens
domain as long as the magnitude and direction field to tune a specific level
transition is stressed
Recent progress with large-scale ab initio calculations: the CONQUEST
  code

While the success of density functional theory (DFT) has led to its use in a
wide variety of fields such as physics, chemistry, materials science and
biochemistry, it has long been recognised that conventional methods are very
inefficient for large complex systems, because the memory requirements scale as
$N^2$ and the cpu requirements as $N^3$ (where $N$ is the number of atoms). The
principles necessary to develop methods with linear scaling of the cpu and
memory requirements with system size ($\mathcal{O}(N)$ methods) have been
established for more than ten years, but only recently have practical codes
showing this scaling for DFT started to appear. We report recent progress in
the development of the \textsc{Conquest} code, which performs $\mathcal{O}(N)$
DFT calculations on parallel computers, and has a demonstrated ability to
handle systems of over 10,000 atoms. The code can be run at different levels of
precision, ranging from empirical tight-binding, through \textit{ab initio}
tight-binding, to full \textit{ab initio}, and techniques for calculating ionic
forces in a consistent way at all levels of precision will be presented.
Illustrations are given of practical \textsc{Conquest} calculations in the
strained Ge/Si(001) system.Comment: 12 pages, 7 figures, accepted by phys. stat. sol.
Quantum fluid effects and parametric instabilities in microcavities

We present a description of the non-equilibrium properties of a microcavity
polariton fluid, injected by a nearly-resonant continuous wave pump laser. In
the first part, we point out the interplay between the peculiar dispersion of
the Bogolubov-like polariton excitations and the onset of polariton parametric
instabilities. We show how collective excitation spectra having no counterpart
in equilibrium systems can be observed by tuning the excitation angle and
frequency. In the second part, we explain the impact of these collective
excitations on the in-plane propagation of the polariton fluid. We show that
the resonant Rayleigh scattering induced by artificial or natural defects is a
very sensitive tool to show fascinating effects such as polariton superfluidity
or polariton Cherenkov effect. We present a comprehensive set of predicted
far-field and near-field images for the resonant Rayleigh scattering emission.Comment: 25 figures, 16 pages lon
Estimation of gloss from rough surface parameters

Gloss is a quantity used in the optical industry to quantify and categorize
materials according to how well they scatter light specularly. With the aid of
phase perturbation theory, we derive an approximate expression for this
quantity for a one-dimensional randomly rough surface. It is demonstrated that
gloss depends in an exponential way on two dimensionless quantities that are
associated with the surface randomness: the root-mean-square roughness times
the perpendicular momentum transfer for the specular direction, and a
correlation function dependent factor times a lateral momentum variable
associated with the collection angle. Rigorous Monte Carlo simulations are used
to access the quality of this approximation, and good agreement is observed
over large regions of parameter space.Comment: 5 page
Quantum fluctuations of the ultracold atom-molecule mixtures

We investigate evolution of the quantum coherence in the ultracold mixture of
fermionic atoms and bosonic dimer molecules. Interactions are there
experimentally controlled via tuning the external magnetic field. Consequently,
the fermionic atoms and their bosonic counterparts can be driven to a behavior
resembling the usual BCS to BEC crossover. We analyze in some detail how this
quantum coherence evolves with respect to time upon a smooth and abrupt sweep
across the Feshbach resonance inducing the atom-molecule quantum fluctuations.Comment: 4 pages, 2 figure
Half-filled stripes in the t-t'-U Hubbard model

Using a self-consistent Hartree-Fock approximation we investigate the
relative stability of various stripe phases in the extended $t$-$t'$-$U$
Hubbard model. One finds that a negative ratio of next- to nearest-neighbor
hopping $t'/t<0$ expells holes from antiferromagnetic domains and reinforces
the stripe order. Therefore the half-filled stripes not only accommodate holes
but also redistribute them so that the kinetic energy is gained, and these
stripes take over in the regime of $t'/t\simeq -0.3$ appropriate for
YBa$_2$Cu$_3$O$_{6+\delta}$.Comment: Accepted for publication in Phys. Stat. So
Gossamer Superconductivity, New Paradigm?

We shall review our recent works on d-wave density wave (dDW) and gossamer
superconductivity (i.e. d-wave superconductivity in the presence of dDW) in
high-T$_{c}$ cuprates and CeCoIn$_{5}$. a) We show that both the giant Nernst
effect and the angle dependent magnetoresistance (ADMR) in the pseudogap phases
of the cuprates and CeCoIn$_{5}$ are manifestations of dDW. b) The phase
diagram of high-T$_{c}$ cuprates is understood in terms of mean field theory,
which includes two order parameters $\Delta_{1}$ and $\Delta_{2}$, where one
order parameter is from dDW and the other from d-wave superconductivity. c) In
the optimally to the overdoped region we find the spatially periodic dDW, an
analogue of the Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) state, becomes more
stable. d) In the underdoped region where $\Delta_{2}/\Delta_{1} \ll 1$ the
Uemera relation is obtained within the present model. We speculate that the
gossamer superconductivity is at the heart of high-T$_{c}$ cuprate
superconductors, the heavy-fermion superconductor CeCoIn$_{5}$ and the organic
superconductors $\kappa$- (ET)$_{2}$Cu(NCS)$_{2}$ and (TMTSF)$_2$PF$_{6}$
Magnetic and superconducting correlations in the two-dimensional Hubbard
  model

The interplay and competition of magnetic and superconducting correlations in
the weakly interacting two-dimensional Hubbard Model is investigated by means
of the functional renormalization group. At zero temperature the flow of
interactions in one-loop approximation evolves into a strong coupling regime at
low energy scales, signalling the possible onset of spontaneous symmetry
breaking. This is further analyzed by a mean-field treatment of the strong
renormalized interactions which takes into account magnetic and superconducting
order simultaneously. The effect of strong correlations on single-particle
properties in the normal phase is studied by calculating the flow of the
self-energy.Comment: 16 pages, 10 figure
New magnetostatic modes in small nonellipsoidal magnetic particles

Magnetostatic normal modes are investigated here in elongated rods. The
dipolar field resulting from the dipole-dipole interactions is calculated
numerically in points of the axis connecting opposite rod face centers
(\emph{central axis}) by collecting individual contributions to this field
coming from each of the atomic planes perpendicular to the central axis. The
applied magnetic field is assumed to be oriented along the central axis, and
the magnetization to be uniform throughout the sample. The \emph{frequency}
spectrum of magnetostatic waves propagating in the direction of the applied
field is found numerically by solving the Landau-Lifshith equation of motion
with the spatially \emph{nonhomogeneous} dipolar field taken into account; the
mode amplitude \emph{profiles} are depicted as well. While energetically
highest modes have \emph{bulk-extended} character, the modes forming the lower
part of the spectrum are localized in the subsurface region (\emph{bulk-dead
modes}). Between these two mode types, magnetostatic modes of a new type
(\emph{comb modes}) are found to occur, characterized by two clearly
discernible regions: a zone of fast amplitude oscillations inside the rod, and
narrow slow-oscillation regions at the borders. Absorbing virtually no energy
from an applied alternating field, comb modes will have no significant
contribution to the magnetic noise.Comment: 16 pages, 6 figures, conferences paper: Physics of Magnetism'05,
  Poznan, Polan
Orbital-selective Mott transitions in the 2-band J_z-model: a
  high-precision quantum Monte Carlo study

Using high-precision quantum Monte Carlo (QMC) simulations within the
framework of dynamical mean field theory (DMFT), we show that the anisotropic
degenerate two-orbital Hubbard model contains two consecutive orbital-selective
Mott transitions (OSMTs) even in the absence of spin-flip terms and
pair-hopping processes. In order to reveal the second transition we carefully
analyze the low-frequency part of the self-energy and the local spectral
functions. This paper extends our previous work to lower temperatures. We
discuss the nature - in particular the order - of both Mott transitions and
list various possible extensions.Comment: 4 pages, pss style; presented at conference "Physics of Magnetism",
  Poznan (Poland), June 24-27, 200
Electronic structure and parity effects in correlated nanosystems

We discuss the spectral, transport and magnetic properties of quantum
nanowires composed of N\leq 13 atoms and containing either even or odd numbers
of valence electrons. In our approach we combine Exact Diagonalization and Ab
Initio calculations (EDABI method). The analysis is performed as a function of
the interatomic distance. The momentum distribution differs drastically for
those obtained for even N with those for odd N, whereas the Drude weight
evolves smoothly. A role of boundary conditions is stressed.Comment: 4 pages, 3 figure