pinecone/core-2020-05-10-deduplication huggingface dataset:
Spin-charge rotating local reference frames: a unified U(2)=U(1)xSU(2)
  approach to the interacting electrons

A spin-charge unifying description for the Hubbard model based on the time
dependent local gauge transformations is developed. The collective variables
for charge and spin are isolated in the form of the space-time fluctuating U(1)
phase field and rotating spin quantization axis governed by the SU(2) symmetry,
respectively. As a result interacting electrons appear as a composite objects
consisting of bare fermions with attached U(1) and SU(2) gauge fields. We
elaborate on the microscopic origins of the effective action with the Coulomb
interaction that contain topological theta terms. Furthermore, we unravel the
link between non-trivial multiply-connected topological structure of the
U(2)=U(1)$\otimes$SU(2) configurational space for gauge fields and the
instanton contribution to the statistical sum.Comment: 5 pages, Proceedings of the XXX International Conference of
  Theoretical Physics: Electron Correlations in nano- and macrosystems (ECNM06
  Ustron, Poland); to be published in Phys. Stat. Solidi
Study of transport properties of a molecular junction as a function of
  distance between the leads

We consider a model of a molecular junction made of BDT (benzene dithiol)
molecule trapped between two Au(100) leads. Using the ab initio approach
implemented in the SIESTA package we look for the optimal configuration of the
molecule as a function of a distance between the leads. We find that for the
distance long enough the energy of the system is minimized when the molecule is
bonded asymmetricaly, i.e. chemisorbed to one of the leads, whereas for the
distance shorter than 12 \AA the energy is minimized for the molecule sitting
in the middle between the leads. We discuss possible consequences of the above
findings for the transport properties of the junction
Thermoelectric effects in STM tunneling through a monoatomic chain

We study thermoelectric properties of the system composed of a monoatomic
chain on a surface and additional electrode coupled to the chain, which can be
an STM tip. In particular, we are interested in thermopower, electric and
thermal conductance, Wiedemann-Franz relation and thermoelectric figure of
merit, which is a direct measure of the usefulness of the system for
applications. We discuss the modifications of the STM wire topography due to
temperature gradient between the electrodes. Finally, we also make connection
to STM experiment, in which the thermopower has been directly measured, showing
different structure, not visible in topography spectra.Comment: 5 pages, 3 eps figure
Bottom-up approach to high-temperature superconductivity

Since the discovery of high-temperature superconductivity in the cuprates a
theoretical understanding of their phase diagram has remained one of the major
outstanding problems in condensed matter physics. Here we propose an effective
low-energy Hamiltonian which produces both d-wave density wave (dDW) and d-wave
superconducting (dSC) solutions within the BCS mean-field theory. This model
predicts that (a) the observed pseudogap phase is a dDW state, (b) the
superconducting phase is a d-wave BCS state, and (c) in the underdoped regime
there is a gossamer superconducting state, i.e. dSC in coexistence with dDW.
Moreover, this theory naturally explains the Uemura relation, the reduction of
the quasiparticle density of states at the Fermi level, and the salient
features in the tunneling conductivity measured in underdoped Bi2212
Spin-orbital entanglement near quantum phase transitions

Spin-orbital entanglement in the ground state of a one-dimensional
SU(2)$\otimes$SU(2) spin-orbital model is analyzed using exact diagonalization
of finite chains. For $S=1/2$ spins and $T=1/2$ pseudospins one finds that the
quantum entanglement is similar at the SU(4) symmetry point and in the
spin-orbital valence bond state. We also show that quantum transitions in
spin-orbital models turn out to be continuous under certain circumstances, in
constrast to the discontinuous transitions in spin models with SU(2) symmetry.Comment: 5 pages, 4 figure
Effect of the next-nearest neighbor hopping on the stability and band
  structure of the incommensurate phases in the cuprates

Using a spin-rotation invariant version of the slave-boson approach we
investigate the relative stability and band structure of various incommensurate
phases in the cuprates. Our findings obtained in the Hubbard model with
next-nearest neighbor hopping $-t'/t\simeq 0.15$, as appropriate for the
La$_{2-x}$Sr$_x$CuO$_4$ family, support the formation of diagonal (vertical)
stripe phases in the doping regime $x=1/16$ ($x=1/8$), respectively. In
contrast, based on the fact that a larger value $-t'/t=0.3$ expected for
YBa$_2$Cu$_3$O$_{6+\delta}$ triggers a crossover to the diagonal (1,1) spiral
phase at increasing doping, we argue that it might explain why the static
charge order has been detected in YBa$_2$Cu$_3$O$_{6+\delta}$ only in the
highly underdoped regime.Comment: 5 pages, 5 figure
Quantum gambling using mesoscopic ring qubits

Quantum Game Theory provides us with new tools for practising games and some
other risk related enterprices like, for example, gambling. The two party
gambling protocol presented by Goldenberg {\it et al} is one of the simplest
yet still hard to implement applications of Quantum Game Theory. We propose
potential physical realisation of the quantum gambling protocol with use of
three mesoscopic ring qubits. We point out problems in implementation of such
game.Comment: 4 pages, 1 figure, poster during XXX Intern. Conf. of Theoretical
  Physics, Electron correlations in nano- and microsystems, Ustron 9-14
  September 2006. Minor corrections, references added; to appear in physica
  status solidi
Local structure around Mn in Mn containing ZnO nanocrystals

Among the diluted magnetic semiconductors of current interest, especially ZnO is experiencing a renaissance with the incorporation of Mn because of the recent predictions from theory. We have obtained local structure information from X ray Absorption Spectroscopy  XAS  complementing previous electron paramagnetic resonance  EPR  studies on Mn in ZnO nanocrystals and Zn OH 2. Mn is found to be incorporated substitutionally into the ZnO nanocrystals with a sizeable distortion as compared to the regular ZnO lattice structure. Depending on the preparation of the nanocrystals Mn is found in the ZnO core as well as in a Zn OH  2 surface shell with a fraction which decreases upon annealing as the shell disintegrates forming additional ZnO.  No indications for Mn clusters were foun
Temperature-dependent Raman scattering of natural and isotopically
  substituted PbS

Lead sulfide is an important semiconductor that has found technological
applications for over a century. Raman spectroscopy, a standard tool for the
investigation and characterization of semiconductors, has limited application
to this material because of the forbidden nature of its first order scattering
and its opacity to visible lasers. Nevertheless, useful vibrational spectra
from two-phonon processes are obtained with red lasers, probably because of a
resonance in the concomitant electronic transitions. Here we report temperature
dependent spectra, covering the 10-300 K range, for two samples with different
sulfur isotopic compositions. The results are analyzed by comparison with ab
initio calculations of the lattice dynamics of PbS and the corresponding
densities of one and two-phonon states. Emphasis is placed on the analysis of
the two phonon band centered at ~430 cm-1.Comment: 8 figure
Laterally coupled and field-induced quantum Hall systems

A quantum Hall system which is divided into two laterally coupled subsystems
by means of a tunneling barrier exhibits a complex Landau level dispersion.
Magnetotunneling spectroscopy is employed to investigate the small energy gaps
which separate subsequent Landau bands. The control on the Fermi level permits
to trace the anticrossings for varying magnetic fields. The band structure
calculation predicts a magnetic shift of the band gaps on the scale of the
cyclotron energy. This effect is confirmed experimentally by a displacement of
the conductance peaks on the axis of the filling factor. Tunneling centers
within the barrier are responsible for quantum interferences between opposite
edge channels. Due to the disorder potential, the corresponding Aharonov-Bohm
interferometers generate additional long-period and irregular conductance
features. In the regime of strong localization, conductance fluctuations occur
at small magnetic fields before the onset of the regular Landau oscillations.
The Landau dispersion is obtained by a dedicated algorithm which solves the
Schroedinger equation exactly for a single electron residing in a quantum Hall
system with an arbitrary unidirectional, threefold staircase potential.Comment: 20 pages, 11 figures, 1 table; v2: explanation added in section 2,
  some minor change
Flux-biased mesoscopic rings

Kinetics of magnetic flux in a thin mesoscopic ring biased by a strong
external magnetic field is described equivalently by dynamics of a Brownian
particle in a tilted washboard potential. The 'flux velocity', i.e. the
averaged time derivative of the total magnetic flux in the ring, is a candidate
for a novel characteristics of mesoscopic rings. Its global properties reflect
the possibility of accommodating persistent currents in the ring.Comment: 7 pages, 4 figures, Presented at the XXII International Conference of
  Theoretical Physics - Electron Correlations in Nano- and Macrosystems, 9 - 14
  September 2006, Ustron, Poland; phys. stat. sol. (b) (in press) (2007
Partial localization of correlated electrons: spin dependent masses,
  saturated ferromagnetism, and effective s-d model

We determine the localization threshold in a partially filled and orbitally
degenerate model of correlated electrons. Particular emphasis is put on a
non-integer band filling, when the system decomposes into the localized and the
itinerant subsystems; this situation is described by an effective s-d model. A
simultaneous transition to the ferromagnetic state is discussed as driven by
the Hund's rule coupling. Dependence of the quasiparticle mass on the spin
direction appears naturally in the ferromagnetic phase and is attributed to the
electron correlation effects, as is also a metamagnetic transition in an
applied field. Although the main results have been obtained within the saddle
point slave-boson approach, their qualitative features are discussed in general
terms, i.e. as a transition from quantum-mechanical indistinguishability of
particles to the two-component situation. A comparison with the situation for
the orbitally nondegenerate band is also briefly mentioned.Comment: 9 pages, 7 figure
Ultralong-range radiative excitation transfer between quantum dots in a
  planar microcavity

We study the system of two quantum dots lying on the central plane of a
planar semiconductor microcavity. By solving the full Maxwell problem, we
demonstrate that the rate of resonant excitation transfer between the two dots
decays as $d^{-1/2}$ as a function of the distance $d$ at long distance. This
very long-range mechanism is due to the leaky and guided modes of the
microcavity, which act as effective radiative transfer channels. At short
distance, the $d^{-3}$ dependence of the F\"orster mechanism, induced by the
electrostatic dipole-dipole interaction, is recovered
Is thermal conductivity time-dependent?

The question whether thermal conductivity may be time dependent on short time scales is investigated and answered in the affirmative. For this purpose, we make use of a classical relation between the Brownian mean displacement and the thermal conductivity. Interest-ingly, the transition from the time dependent regime to stationary behaviour is in the vicinity of Allen’s temperature relaxation time. Calculation of the electronic temperature, when the new time dependent thermal conductivity is used, shows an improvement in the re-sults derived by means of the two-temperature model. Furthermore, the Wiedemann-Franz law is not valid in the time regime investigated
Non-DMS related ferromagnetism in transition metal doped zinc oxide

We review pitfalls in recent efforts to make a conventional semiconductor,
namely ZnO, ferromagnetic by means of doping with transition metal ions. Since
the solubility of those elements is rather low, formation of secondary phases
and the creation of defects upon low temperature processing can lead to
unwanted magnetic effects. Among others, ion implantation is a method of
doping, which is highly suited for the investigation of those effects. By
focussing mainly on Fe, Co or Ni implanted ZnO single crystals we show that
there are manifold sources for ferromagnetism in this material which can easily
be confused with the formation of a ferromagnetic diluted magnetic
semiconductor (DMS). We will focus on metallic as well as oxide precipitates
and the difficulties of their identification.Comment: 24 pages, 22 figure
Electron beam induced electronic transport in alkyl amine-intercalated VOx nanotubes

The electron beam induced electronic transport in primary alkyl amine-intercalated V2O5 nanotubes is investigated where the organic amine molecules are employed as molecular conductive wires to an aminosilanized substrate surface and contacted to Au interdigitated electrode contacts. The results demonstrate that the high conductivity of the nanotubes is related to the non-resonant tunnelling through the amine molecules and a reduced polaron hopping conduction through the vanadium oxide itself. Both nanotube networks and individual nanotubes exhibit similarly high conductivities where the minority carrier transport is bias dependent and nanotube diameter invariant
Kondo effects in a C_60 single-molecule transistor

We have used the electromigration technique to fabricate a
  $\rm{C_{{60}}}$ single-molecule transistor (SMT). We present a full
experimental study as a function of temperature, down to 35 mK, and as a
function of magnetic field up to 8 T in a SMT with odd number of electrons,
where the usual spin-1/2 Kondo effect occurs, with good agreement with theory.
In the case of even number of electrons, a low temperature magneto-transport
study is provided, which demonstrates a Zeeman splitting of the zero-bias
anomaly at energies well below the Kondo scale.Comment: 4 pages, 3 figure
Truss-type systems exhibiting negative compressibility

We propose novel two- and three-dimensional truss structures made from rods of different materials connected together through pin-joints to form triangular units which can exhibit anomalous compressibility properties. In particular, we show that these systems may be made to exhibit negative linear compressibility along certain directions or compressibilities that are even more positive than any of the component materials, i.e. the end product is a system with tunable compressibility properties that can be tailor made for particular practical applications. We also show that in specific cases, these systems can exhibit an overall negative area compressibility and sometimes even negative volumetric compressibility (i.e. negative bulk modulus) thus confirming that this property can indeed exist.peer-reviewe
Generalizing Planck's Law: Nonequilibrium Emission of Excited Media

Using a quantum-kinetic many-body approach, exact results for the interacting
system of field and matter in a specified geometry are presented. It is shown
that both the spectral function of photons and the field fluctuations split up
into vacuum- and medium-induced contributions, for which explicit expressions
are derived. Using Poynting's theorem, the incoherent emission is analyzed and
related to the coherent absorption as may be measured in a linear
transmission-reflection experiment. Their ratio defines the medium-induced
population of the modes of the transverse electromagnetic field and so
generalizes Planck's law to an arbitrarily absorbing and dispersing medium in a
nonequilibrium steady state. For quasi-equilibrium, this population develops
into a Bose distribution whose chemical potential marks the crossover from
absorption to gain and, also, characterizes the degree of excitation.
Macroscopic quantum phenomena such as lasing and quantum condensation are
discussed on this footing.Comment: minor corrections and extended discussion, as publishe
Current Density Functional Theory for one-dimensional fermions

The frequency-dependent response of a one-dimensional fermion system is
investigated using Current Density Functional Theory (CDFT) within the local
approximation (LDA). DFT-LDA, and in particular CDFT-LDA, reproduces very well
the dispersion of the collective excitations. Unsurprisingly, however, the
approximation fails for details of the dynamic response for large wavevectors.
In particular, we introduce CDFT for the one-dimensional spinless fermion model
with nearest-neighbor interaction, and use CDFT-LDA plus exact (Bethe ansatz)
results for the groundstate energy as function of particle density and boundary
phase to determine the linear response. The successes and failures of this
approach are discussed in detail
Theoretical description of time-resolved pump/probe photoemission in
  TaS\_2: a single-band DFT+DMFT(NRG) study within the quasiequilibrium
  approximation

In this work, we theoretically examine recent pump/probe photoemission
experiments on the strongly correlated charge-density-wave insulator TaS\_2. We
describe the general nonequilibrium many-body formulation of time-resolved
photoemission in the sudden approximation, and then solve the problem using
dynamical mean-field theory with the numerical renormalization group and a bare
density of states calculated from density functional theory including the
charge-density-wave distortion of the ion cores and spin-orbit coupling
  We find a number of interesting results: (i) the bare band structure actually
has more dispersion in the perpendicular direction than in the two-dimensional
planes; (ii) the DMFT approach can produce upper and lower Hubbard bands that
resemble those in the experiment, but the upper bands will overlap in energy
with other higher energy bands; (iii) the effect of the finite width of the
probe pulse is minimal on the shape of the photoemission spectra; and (iv) the
quasiequilibrium approximation does not fully describe the behavior in this
system.Comment: (7 pages, 5 figures, proceedings for Coherence and correlations in
  nanosystems conference, September 5-10, Ustron, Poland
Recent progress in open quantum systems: Non-Gaussian noise and
  decoherence in fermionic systems

We review our recent contributions to two topics that have become of interest
in the field of open, dissipative quantum systems: non-Gaussian noise and
decoherence in fermionic systems. Decoherence by non-Gaussian noise, i.e. by an
environment that cannot be approximated as a bath of harmonic oscillators, is
important in nanostructures (e.g. qubits) where there might be strong coupling
to a small number of fluctuators. We first revisit the pedagogical example of
dephasing by classical telegraph noise. Then we address two models where the
quantum nature of the noise becomes essential: "quantum telegraph noise" and
dephasing by electronic shot noise. In fermionic systems, many-body aspects and
the Pauli principle have to be taken care of when describing the loss of phase
coherence. This is relevant in electronic quantum transport through metallic
and semiconducting structures. Specifically, we recount our recent results
regarding dephasing in a chiral interacting electron liquid, as it is realized
in the electronic Mach-Zehnder interferometer. This model can be solved
employing the technique of bosonization as well as a physically transparent
semiclassical method.Comment: Proceedings of Ustron 2008 conference, 6 pages, 3 figure
Current-induced spin polarization for a general two-dimensional electron
  system

In this paper, current-induced spin polarization for two-dimensional electron
gas with a general spin-orbit interaction is investigated. For isotropic energy
spectrum, the in-plane current-induced spin polarization is found to be
dependent on the electron density for non-linear spin-orbit interaction and
increases with the increment of sheet density, in contrast to the case for $\bm
k$-linear spin-orbit coupling model. The numerical evaluation is performed for
InAs/InSb heterojunction with spin-orbit coupling of both linear and cubic
spin-orbit coupling types. For $\delta$-type short-range electron-impurity
scattering, it is found that the current-induced spin polarization increases
with increasing the density when cubic spin-orbit couplings are considered.
However, for remote disorders, a rapid enhancement of current-induced spin
polarization is always observed at high electron density, even in the case
without cubic spin-orbit coupling. This result demonstrates the
collision-related feature of current-induced spin polarization. The effects of
different high order spin-orbit couplings on spin polarization can be
comparable.Comment: 5 pages, 3 figure
Optical Properties of Correlated Materials -- or Why Intelligent Windows
  may look Dirty

Materials with strong electronic Coulomb correlations play an increasing role
in modern materials applications. "Thermochromic" systems, which exhibit
thermally induced changes in their optical response, provide a particularly
interesting case. The optical switching associated with the metal-insulator
transition of vanadium dioxide, for example, has been proposed for use in
numerous applications, ranging from anti-laser shields to "intelligent"
windows, which selectively filter radiative heat in hot weather conditions. Are
present-day electronic structure techniques able to describe, or -- eventually
even predict -- such a kind of behavior ? How far are we from materials design
using correlated oxides ? These are the central questions we try to address in
this article. We review recent attempts of calculating optical properties of
correlated materials within dynamical mean field theory, and summarize results
for vanadium dioxide obtained within a novel scheme aiming at particularly
simple and efficient calculations of optical transition matrix elements within
localized basis sets. Finally, by optimizing the geometry of "intelligent
windows", we argue that this kind of technique can in principle be used to
provide guidance for experiments, thus giving a rather optimistic answer to the
above questions.Comment: 11 pages, 4 figures, Phys. Status Solidi B 246, in print (2009), also
  available as psi-k Scientific Highlight of the Month, no. 88, August 2008,
  http://www.psi-k.org/newsletters/News_88/Highlight_88.pd