pinecone/core-2020-05-10-deduplication huggingface dataset:
Bloch waves of small high-Tc bipolarons

Over the last decade several competing models of high-temperature
superconductivity were proposed, most of them with short-range interactions. We
review a more realistic model with strong on-site repulsive correlations, the
Coulomb and strong finite-range electron-phonon interactions. Bipolarons in the
model exist in the itinerant Bloch states at temperatures below about half of
the characteristic phonon frequency. Depending on the ratio of the inter-site
Coulomb repulsion and the polaron level shift the ground state of the model is
a polaronic Fermi (or Luttinger) liquid, bipolaronic high-Tc superconductor, or
charge-segregated insulator for the strong, intermediate, and weak Coulomb
repulsion, respectively. Two particular lattices are analysed in detail: a
chain with the finite range electron-phonon interaction and a zig-zag ladder.
Charge carriers in the ladder are superlight mobile intersite bipolarons. They
propagate coherently without emission or absorption of phonons with about the
same mass as single polarons. The model describes key features of the cuprates,
in particular their Tc values, different isotope effects, normal state
pseudogaps, and spectral functions measured in tunnelling and photoemission.Comment: 25 pages, 2 figures, invited paper to Festschrift in honor of
  Professor J.T. Devrees
Superconducting nanobridges under magnetic fields

We report on the study of superconducting nanotips and nanobridges of lead
with a Scanning Tunnelling Microscope in tunnel and point contact regimes. We
deal with three different structures. A nanotip that remains superconducting
under a field of 2 T. For this case we present model calculations of the order
parameter, which are in good agreement with the experiments. An asymmetric
nanobridge of lead showing a two steps loss of the Andreev excess current due
to different heating and dissipation phenomena in each side of the structure. A
study of the effect of the thermal fluctuations on the Josephson coupling
between the two sides of a superconducting nanobridge submitted to magnetic
fields. The different experiments were made under magnetic fields up to twenty
five times the volume critical field of lead, and in a temperature range
between 0.6 K and 7.2 K.Comment: 17 pages, 7 figure
Spin dephasing in n-typed GaAs quantum wells in the presence of high
  magnetic fields in Voigt configuration

We perform a many-body study of the spin dephasing due to the
D'yakonov-Perel' effect in n-typed GaAs (100) quantum wells under high magnetic
fields in the Voigt configuration by constructing and numerically solving the
kinetic Bloch equations. We include all the spin conserving scattering such as
electron-phonon, the electron-nonmagnetic impurity as well as the
electron-electron Coulomb scattering in our theory and investigate how the spin
dephasing time (SDT) is affected by the initial spin polarization, impurity,
and magnetic field.
  The dephasing obtained from our theory contains not only that due to the
effective spin-flipping scattering first proposed by D'yakonov and Perel' [Zh.
Eksp. Teor. Fiz. {\bf 60}, 1954 (1971)[Sov. Phys.-JETP {\bf 38}, 1053 (1971)]],
but also the recently proposed many-body dephasing due to the inhomogeneous
broadening provided by the DP term [Wu, J. Supercond.:Incorp. Novel Mechanism
{\bf 14}, 245 (2001); Wu and Ning, Eur. Phys. J. B {\bf 18}, 373 (2000)]. We
are able to investigate the spin dephasing with extra large spin polarization
(up to 100 %) which has not been discussed both theoretically and
experimentally. A huge anomalous resonance of the SDT for large spin
polarizations is predicted under the high magnetic field we used.Comment: 8 pages, Revtex, 7 figures in EPS forma
KP-approach for non-symmetric short-range defects: resonant states and
  alloy bandstructure

The short-range defect with reduced symmetry is studied in the framework of
KP-approach taking into account a matrix structure of potential energy in the
equations for envelope functions. The case of the narrow-gap semiconductor,
with defects which are non-symmetric along the [001], [110], or [111]
directions, is considered. Resonant state at a single defect is analyzed within
the Koster-Slater approximation. The bandstructure modification of the alloy,
formed by non-symmetric impurities, is discussed and a generalized virtual
crystal approximation is introduced.Comment: Extended version, 9 pages, 6 figures (EPS
Horizontal line nodes in superconducting Sr2RuO4

We analyze the possibilities of triplet pairing in Sr2RuO4 based upon an idea
of interlayer coupling. We have considered two models differing by the
effective interactions. In one model the quasi-particle spectra have horizontal
line nodes on all three Fermi surface sheets, while in the other the spectra
have line or point nodes on the alpha and beta sheets and no nodes on the gamma
sheet. Both models reproduce the experimental heat capacity and penetration
depth results, but the calculated specific heat is sightly closer to experiment
in the second solution with nodes only on the alpha and beta sheets.Comment: 9 pages, 6 figure
Fragmentation of multiply charged simple metal clusters in liquid-drop
  stabilized jellium model

In this work, we have used the liquid-drop model in the context of stabilized
jellium model, to study the stability of $Z$-ply charged metal clusters of
different species against fragmentation. We have shown that on the one hand,
singly ionized clusters are stable against any spontaneous fragmentation, and
on the other hand, the most favored decay process for them is atomic
evaporation. However, multiply charged clusters of sufficiently small sizes may
undergo spontaneous decay via fission processes. Comparing the results for
different species show that for fixed $N$, the lower electron density metal
clusters can accommodate more excess charges before their Coulomb explosions.
This comparison also shows that, for fixed $Z$, the atomic evaporation which is
the most favored decay mechanism for sufficiently large clusters, takes place
at lower $N$s for lower electron density clusters.Comment: 11 pages, 24 ps figure
Charge Transfer and Charge Transport on the Double Helix

We present a short review of various experiments that measure charge transfer
and charge transport in DNA. Some general comments are made on the possible
connection between 'chemistry-style' charge transfer experiments that probe
fluorescence quenching and remote oxidative damage and 'physics-style'
measurements that measure transport properties as defined typically in the
solid-state. We then describe measurements performed by our group on the
millimeter wave response of DNA. By measuring over a wide range of humidity
conditions and comparing the response of single strand DNA and double strand
DNA, we show that the appreciable AC conductivity of DNA is not due to photon
assisted hopping between localized states, but instead due to dissipation from
dipole motion in the surrounding water helix.Comment: 7 pages, 3 figure
Shot Noise in Mesoscopic Transport Through Localised States

We show that shot noise can be used for studies of hopping and resonant
tunnelling between localised electron states. In hopping via several states,
shot noise is seen to be suppressed compared with its classical Poisson value
$S_I=2eI$ ($I$ is the average current) and the suppression depends on the
distribution of the barriers between the localised states. In resonant
tunnelling through a single impurity an enhancement of shot noise is observed.
It has been established, both theoretically and experimentally, that a
considerable increase of noise occurs due to Coulomb interaction between two
resonant tunnelling channels.Comment: 7 pages, 5 figures; Proceedings of the 10th Conference on Hopping and
  Related Phenomena (Trieste 2003); requires Wiley style files (included
Magnetic energy-level diagrams of high-spin (Mn$_{12}$-acetate) and
  low-spin (V$_{15}$) molecules

The magnetic energy-level diagrams for models of the Mn12 and V15 molecule
are calculated using the Lanczos method with full orthogonalization and a
Chebyshev-polynomial-based projector method. The effect of the
Dzyaloshinskii-Moriya interaction on the appearance of energy-level repulsions
and its relevance to the observation of steps in the time-dependent
magnetization data is studied. We assess the usefulness of simplified models
for the description of the zero-temperature magnetization dynamics
Magnetic properties of Co/Ag/Co films grown on Ag(100) nanometer-scale islands

[[abstract]]Self-assembled Ag(100) islands on Si(100) substrate were fabricated by using the molecular beam epitaxy technique. Co/Ag/Co films were then grown onto Ag films at 100 蚓. We have experimentally demonstrated that the magnetic behavior of Co/Ag/Co films is strongly dependent on the thickness and morphology of the Ag(100) islands that serve as a buffer layer. The buffer layer designed to reduce the surface free energy forms isolated pyramidal islands with {111} sidewalls on the Si(100) substrate, and provides feasibility to study the correlation between magnetic properties and interface roughness. Ag islands also play an important role in the magnetoresistance transition of Co/Ag/Co films. The roughened Ag(100) surface facilitates texture growth of Co/Ag/Co films and provides a resultant domain-wall-pinning, that in turn contributes to the in-plane demagnetization factor.[[fileno]]2020336010006[[department]]材料科學工程學
Nitrides as spintronic materials

A report of progress in spintronics-related works involving group III
nitrides is given emphasizing contradictory opinions concerning basics
characteristics of these materials. The actual position of magnetic impurities
in the GaN lattice as well as a possible role of magnetic precipitates is
discussed. The question whether the hole introduce by the Mn impurities is
localized tightly on the Mn d-levels or rather on the hybridized p-d bonding
states is addressed. The nature of spin-spin interactions and magnetic phases,
as provided by theoretical and experimental findings, is outlined, and possible
origins of the high temperature ferromagnetism observed in (Ga,Mn)N are
presented. Experimental studies aiming at evaluating characteristic times of
spin coherence and dephasing in GaN are described.Comment: 6 pages, 9 figures, 5th International Conference on Nitride
  Semiconductors, Nara, May 2003, phys. stat. solid
Polarization behavior in systems with competing ferroelectric and antiferroelectric interactions

The dielectric hysteresis loop constitutes the main feature indicative of the properties of a ferroelectric material, but in complex systems with ferro- and antiferroelectric interactions, the hysteresis loops are often multiple. In the present work, we introduce a model based on the coexistence of ferro- and antiferroelectric regions, which can describe the aforementioned multiple loops. Based on our model, simulated multiple hysteresis loops are in good agreement with experimental results. Hysteresis loops obtained from our model are sensitive to the relative values of the ferro- and antiferroelectric coupling constants, domain size, and temperature. The model describes well systems without the presence of frustration as it is the case of BA(x)BP(1-x). In the case of systems exhibiting frustration like e.g. Rb-x (NH4)(1-x) H2PO4, we present a straightforward extension of our model.Fundação para a Ciência e a Tecnologia (FCT) - Programa Operacional "Ciência, Tecnologia, Inovação" (POCTI) - POCTI/CTM/41574/2001 - Computational Nanophysics (AC), POCTI/CTM/33501/9
From a local Green function to molecular charge transport

A local-orbital based ab initio approach to obtain the Green function for
large heterogeneous systems is developed. First a Green function formalism is
introduced based on exact diagonalization. Then the self energy is constructed
from an incremental scheme, rendering the procedure feasible, while at the same
time physical insight into different local correlation contributions is
obtained. Subsequently the Green function is used in the frame of the Landauer
theory and the wide band approximation to calculate the electronic transmission
coefficient across molecular junctions. The theory is applied to meta- and
para-ditholbenzene linked to gold electrodes and various correlation
contributions are analyzed
Critical properties in long-range hopping Hamiltonians

Some properties of $d$-dimensional disordered models with long-range random
hopping amplitudes are investigated numerically at criticality. We concentrate
on the correlation dimension $d_2$ (for $d=2$) and the nearest level spacing
distribution $P_c(s)$ (for $d=3$) in both the weak ($b^d \gg 1$) and the strong
($b^d \ll 1$) coupling regime, where the parameter $b^{-d}$ plays the role of
the coupling constant of the model. It is found that (i) the extrapolated
values of $d_2$ are of the form $d_2=c_db^d$ in the strong coupling limit and
$d_2=d-a_d/b^d$ in the case of weak coupling, and (ii) $P_ (s)$ has the
asymptotic form $P_c(s)\sim\exp (-A_ds^{\alpha})$ for $s\gg $, with the
critical exponent $\alpha=2-a_d/b^d$ for $b^d \gg 1$ and $\alpha=1+c_d b^d$ for
$b^d \ll 1$. In these cases the numerical coefficients $A_d$, $a_d$ and $c_d$
depend only on the dimensionality.Comment: 9 pages, 6 .eps figures, contribution to the Festschrift for Michael
  Schreiber's 50th birthda
Conservation laws in disordered electron systems: Thermodynamic limit
  and configurational averaging

We discuss conservation of probability in noniteracting disordered electron
systems. We argue that although the norm of the electron wave function is
conserved in individual realizations of the random potential, we cannot extend
this conservation law easily to configurationally averaged systems in the
thermodynamic limit. A direct generalization of the norm conservation to
averaged functions is hindered by the existence of localized states breaking
translational invariance. Such states are elusive to the description with
periodic Bloch waves. Mathematically this difficulty is manifested through the
diffusion pole in the electron-hole irreducible vertex. The pole leads to a
clash with analyticity of the self-energy, reflecting causality of the theory,
when norm conservation is enforced by the Ward identity between one- and
two-particle averaged Green functions.Comment: REVTeX4, 8 pages, no figure
Exponents of the localization length in the 2D Anderson model with
  off-diagonal disorder

We study Anderson localization in two-dimensional systems with purely
off-diagonal disorder. Localization lengths are computed by the transfer-matrix
method and their finite-size and scaling properties are investigated. We find
various numerically challenging differences to the usual problems with diagonal
disorder. In particular, the divergence of the localization lengths close to
the band centre is investigated in detail for bipartite and non-bipartite
lattices as well as different distributions of the off-diagonal disorder.
Divergence exponents for the localization lengths are constructed that appear
to describe the data well down to at least 10^-5. We find only little evidence
for a crossover energy scale below which the power law has been argued to fail.Comment: 10 pages, 9 figures, uses PSS style files (included), submitted to
  phys. stat. sol. (b
Critical points and quenched disorder: From Harris criterion to rare
  regions and smearing

We consider the influence of quenched spatial disorder on phase transitions
in classical and quantum systems. We show that rare strong disorder
fluctuations can have dramatic effects on critical points. In classical systems
with sufficiently correlated disorder or in quantum systems with overdamped
dynamics they can completely destroy the sharp phase transition by smearing.
This is caused by effects similar to but stronger than Griffiths phenomena:
True static order can develop on a rare region while the bulk system is still
in the disordered phase. We discuss the thermodynamic behavior in the vicinity
of such a smeared transition using optimal fluctuation theory, and we present
numerical results for a two-dimensional model system.Comment: 10 pages, 5 eps figures, contribution to the Festschrift for Michael
  Schreiber's 50th birthday, final version as publishe
Relationship between and implications of the isotope and pressure
  effects on transition temperature, penetration depths and conductivities

It is shown that the empirical relations between transition temperature,
normal state conductivity linearly extrapolated to the value at the transition
temperature, zero temperature penetration depths, etc., as observed in a rich
variety of cuprate superconductors, are remarkably consistent with the
universal critical properties of anisotropic systems which fall into the 3D-XY
universality class and undergo a crossover to a quantum critical point in 2D.
The variety includes n- and p-type cuprates, comprises the underdoped and
overdoped regimes and the consistency extends up to six decades in the scaling
variables. The resulting scaling relations for the oxygen isotope and
hydrostatic pressure effects agree with the experimental data and reveal that
these effects originate from local lattice distortions preserving the volume of
the unit cell. These observations single out 3D and anisotropic microscopic
models which incorporate local lattice distortions, fall in the experimentally
accessible regime into the 3D-XY universality class, and incorporate the
crossover to 2D quantum criticality where superconductivity disappears.Comment: 19 pages, 17 figure
Light scattering of double wall carbon nanotubes under hydrostatic pressure: pressure effects on the internal and external tubes

We report high-pressure Raman light scattering studies up to 10 GPa on double walled carbon nanotubes using two pressure transmitting media. In alcohol, a clear splitting of the G band is observed up to 10 GPa. This splitting is evidence for both discontinuous tangential stress and continuous radial stress. A structural distortion seems to be present at 3 GPa, revealed by a spectroscopic signature at 1480 cm–1. With argon as the pressure transmitting medium, the nanotubes bundles show a transition at 6 GPa which corresponds to a collapse to a flattened structure and removes the splitting. The comparison of the pressure coefficients before the transition for the two pressure transmitting media shows that the ratio of the two coefficients associated with internal and external tubes, is the same but the absolute values are different
Hydrostatic Pressure Effects on the Structural and Electronic Properties
  of Carbon Nanotubes

We study the structural and electronic properties of isolated single-wall
carbon nanotubes (SWNTs) under hydrostatic pressure using a combination of
theoretical techniques: Continuum elasticity models, classical molecular
dynamics simulations, tight-binding electronic structure methods, and
first-principles total energy calculations within the density-functional and
pseudopotential frameworks. For pressures below a certain critical pressure
$P_c$, the SWNTs' structure remains cylindrical and the Kohn-Sham energy gaps
of semiconducting SWNTs have either positive or negative pressure coefficients
depending on the value of $(n,m)$, with a distinct "family" (of the same $n-m$)
behavior. The diameter and chirality dependence of the pressure coefficients
can be described by a simple analytical expression. At $P_c$,
molecular-dynamics simulations predict that isolated SWNTs undergo a
pressure-induced symmetry-breaking transformation from a cylindrical shape to a
collapsed geometry. This transition is described by a simple elastic model as
arising from the competition between the bond-bending and $PV$ terms in the
enthalpy. The good agreement between calculated and experimental values of
$P_c$ provides a strong support to the ``collapse'' interpretation of the
experimental transitions in bundles.Comment: To appear in the Proceedings of the 11th International Conference on
  High Pressure Semiconductor Physics (invited paper
Holstein polaron in two and three dimensions by quantum Monte Carlo

A recently developed quantum Monte Carlo approach to the Holstein model with
one electron [PRB 69, 024301 (2004)] is extended to two and three dimensional
lattices. A moderate sign problem occurs, which is found to diminish with
increasing system size in all dimensions, and not to affect simulations
significantly. We present an extensive study of the influence of temperature,
system size, dimensionality and model parameters on the small-polaron cross
over. Results are extrapolated to remove the error due to the Trotter
discretization, which significantly improves the accuracy. Comparison with
existing work and other quantum Monte Carlo methods is made. The method can be
extended to the many-electron case.Comment: 14 pages, 11 figure
Strongly correlated multilayered nanostructures near the Mott transition

We examine devices constructed out of multilayered sandwiches of
semi-infinite metal--barrier--semi-infinite metal, with the barrier tuned to
lie near the quantum critical point of the Mott metal-insulator transition. By
employing dynamical mean field theory, we are able to solve the many-body
problem exactly (within the local approximation) and determine the density of
states through the nanostructure and the charge transport perpendicular to the
planes. We introduce a generalization of the Thouless energy that describes the
crossover from tunneling to incoherent thermally activated transport.Comment: 7 pages, 6 figures, conference proceedings for the 24th international
  conference in theoretical physics, Ustron, Poland, submitted to phys. stat.
  solidi.
Jahn-Teller effect and electron correlation in alkali doped fullerides

The interplay between Jahn-Teller effect and electron correlation in alkali doped fullerides is reviewed for compounds from both sides of Mott-Hubbard transition. In Mott-Hubbard fullerides the nature of low-lying excitations strongly depends on the symmetry of the compounds, corresponding either to spin (Heisenberg) type for low symmetry compounds (K-3(NH3)C-60) or to spin-vibronic superexchange for cubic compounds (Li-3(NH3)(6)C-60). In the band fullerides (A(3)C(60), A(4)C(60), A = K, Rb) the Jahn-Teller effect leads to a splitting of the cubic band structure in three or two unequally populated subbands (orbital disproportionation), which gives rise to a number of features in the spectroscopy of these compounds. (c) 2005 WILEY-VCH Verlag GmbH T Co. KGTA, Weinheim.status: publishe
Spin-polarized transport through carbon nanotubes

Carbon nanotubes (CNT) belong to the most promising new materials which can
in the near future revolutionize the conventional electronics. When sandwiched
between ferromagnetic electrodes, the CNT behaves like a spacer in conventional
spin-valves, leading quite often to a considerable giant magneto-resistance
effect (GMR). This paper is devoted to reviewing some topics related to
electron correlations in CNT. The main attention however is directed to the
following effects essential for electron transport through nanotubes: (i)
nanotube/electrode coupling and (ii) inter-tube interactions.It is shown that
these effects may account for some recent experimental reports on GMR,
including those on negative (inverse) GMR.Comment: 7 pages, 3 figure