2,674 research outputs found
Causality vs. Ward identity in disordered electron systems
We address the problem of fulfilling consistency conditions in solutions for
disordered noninteracting electrons. We prove that if we assume the existence
of the diffusion pole in an electron-hole symmetric theory we cannot achieve a
solution with a causal self-energy that would fully fit the Ward identity.
Since the self-energy must be causal, we conclude that the Ward identity is
partly violated in the diffusive transport regime of disordered electrons. We
explain this violation in physical terms and discuss its consequences.Comment: 4 pages, REVTeX, 6 EPS figure
Metal-Insulator Transition and Lattice Instability of Paramagnetic V2O3
We determine the electronic structure and phase stability of paramagnetic
VO at the Mott-Hubbard metal-insulator phase transition, by employing a
combination of an ab initio method for calculating band structures with
dynamical mean-field theory. The structural transformation associated with the
metal-insulator transition is found to occur upon a slight expansion of the
lattice volume by %, in agreement with experiment. Our results show
that the structural change precedes the metal-insulator transition, implying a
complex interplay between electronic and lattice degrees of freedom at the
transition. Electronic correlations and full charge self-consistency are found
to be crucial for a correct description of the properties of VO.Comment: 5 pages, 4 figure
A mean-field theory of Anderson localization
Anderson model of noninteracting disordered electrons is studied in high
spatial dimensions. We find that off-diagonal one- and two-particle propagators
behave as gaussian random variables w.r.t. momentum summations. With this
simplification and with the electron-hole symmetry we reduce the parquet
equations for two-particle irreducible vertices to a single algebraic equation
for a local vertex. We find a disorder-driven bifurcation point in this
equation signalling vanishing of diffusion and onset of Anderson localization.
There is no bifurcation in where all states are localized. A natural
order parameter for Anderson localization pops up in the construction.Comment: REVTeX4, 4 pages, 2 EPS figure
Dissipative Currents in Superfluid 3He Weak Links
We calculate the current-pressure relation for pinholes connecting two
volumes of bulk superfluid 3He-B. The theory of multiple Andreev reflections,
adapted from superconducting weak links, leads to a nonlinear dependence of the
dc current on pressure bias. In arrays of pinholes one has to take into account
oscillations of the texture at the Josephson frequency. The associated
radiation of spin waves from the junction leads to an additional dissipative
current at small biases, in quantitative agreement with measurements.Comment: 4 pages, 3 figures; updated to the published versio
Mean-field theories for disordered electrons: Diffusion pole and Anderson localization
We discuss conditions to be put on mean-field-like theories to be able to
describe fundamental physical phenomena in disordered electron systems. In
particular, we investigate options for a consistent mean-field theory of
electron localization and for a reliable description of transport properties.
We argue that a mean-field theory for the Anderson localization transition must
be electron-hole symmetric and self-consistent at the two-particle (vertex)
level. We show that such a theory with local equations can be derived from the
asymptotic limit to high spatial dimensions. The weight of the diffusion pole,
i. e., the number of diffusive states at the Fermi energy, in this mean-field
theory decreases with the increasing disorder strength and vanishes in the
localized phase. Consequences of the disclosed behavior for our understanding
of vanishing of electron diffusion are discussed.Comment: REVTeX4, 11 pages, no figure
Theoretical description of mixed film formation at the air/water interface : carboxylic acids–fatty amines
Thermodynamic parameters of mixed monolayer formation of aliphatic amines CnH2n+1NH2 and carboxylic acids CnH2n+1COOH (n = 6–16) are calculated using the quantum chemical semiempirical PM3 method. Four types of mixed dimers and tetramers amine–acid are considered. The total contribution of interactions between the hydrophilic parts of amine and acid into clusterization Gibbs energy is slightly lower than the corresponding interactions for individual surfactants. It suggests a synergetic interaction between the regarded amphiphilic compounds as proved by experimental data in the literature. Two types of competitive film formation are possible: mixed 2D film 1, where the molecules of the minor component are single distributed among the molecules of the prevailing second component (mixture of components on molecular level), and 2D film 2 with a domain structure comprised of pure component “islands” linked together. The dependence of the Gibbs energy of clusterization per monomer for 2D film 1 on the component mole fraction shows that the maximum synergetic effect is typical for the case that both surfactants have the same even number of carbon atoms in the hydrocarbon chain and form an equimolar mixture. Formation of 2D film 1 is more preferable than that of 2D film 2, if the difference of the hydrocarbon chain lengths is not larger than 5 methylene units. The limiting mole fraction of carboxylic acids in such mixed monolayers is 66.7%
Correlation strength, Lifshitz transition and the emergence of a two- to three-dimensional crossover in FeSe under pressure
We report a detailed theoretical study of the electronic structure, spectral
properties, and lattice parameters of bulk FeSe under pressure using a fully
charge self-consistent implementation of the density functional theory plus
dynamical mean-field theory method (DFT+DMFT). In particular, we perform a
structural optimization and compute the evolution of the lattice parameters
(volume, ratio, and the internal position of Se) and the electronic
structure of the tetragonal (space group ) paramagnetic FeSe. Our
results for the lattice parameters are in good quantitative agreement with
experiment. The ratio is slightly overestimated by about ~\%,
presumably due to the absence of the van der Waals interactions between the
FeSe layers in our calculations. The lattice parameters determined within DFT
are off the experimental values by a remarkable -~\%, implying a
crucial importance of electron correlations. Upon compression to ~GPa, the
ratio and the lattice volume show a decrease by and ~\%,
respectively, while the Se coordinate weakly increases by ~\%.
Most importantly, our results reveal a topological change of the Fermi surface
(Lifshitz transition) which is accompanied by a two- to three-dimensional
crossover. Our results indicate a small reduction of the quasiparticle mass
renormalization by about ~\% for the and less than ~\% for
the states, as compared to ambient pressure. The behavior of the
momentum-resolved magnetic susceptibility shows no topological
changes of magnetic correlations under pressure, but demonstrates a reduction
of the degree of the in-plane stripe-type nesting. Our results for
the electronic structure and lattice parameters of FeSe are in good qualitative
agreement with recent experiments on its isoelectronic counterpart
FeSeS.Comment: 10 pages, 6 figure
Strong-Coupling Effects in "Dirty" Superfluid
The contribution of the strong-coupling effects to the free energy of the
"dirty" superfluid is estimated using a simple model. It is shown that
the strong-coupling effects are less susceptible to the quasiparticle
scattering events in comparison to the weak-coupling counterpart. This supports
the conclusion about stabilization of the -phase in aerogel environment at
pressures where the -phase takes over in bulk superfluid , in
accordance with recent experimental observations in zero magnetic field.Comment: 10 pages, LaTeX file. This is a revised version of the paper with
some additional comments and references, and corrected typos. Submitted to
Journal of Physics: Condensed Matte
Spontaneous mass current and textures of p-wave superfluids of trapped Fermionic atom gases at rest and under rotation
It is found theoretically based on the Ginzburg-Landau framework that p-wave
superfluids of neutral atom gases in three dimension harmonic traps exhibit
spontaneous mass current at rest, whose direction depends on trap geometry.
Under rotation various types of the order parameter textures are stabilized,
including Mermin-Ho and Anderson-Toulouse-Chechetkin vortices. In a cigar shape
trap spontaneous current flows longitudial to the rotation axis and thus
perpendicular to the ordinary rotational current. These features, spontaneous
mass current at rest and texture formation, can be used as diagnoses for p-wave
superfluidity.Comment: 5 pages, 5 figure
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