934 research outputs found
Fermi Edge Resonances in Non-equilibrium States of Fermi Gases
We formulate the problem of the Fermi Edge Singularity in non-equilibrium
states of a Fermi gas as a matrix Riemann-Hilbert problem with an integrable
kernel. This formulation is the most suitable for studying the singular
behavior at each edge of non-equilibrium Fermi states by means of the method of
steepest descent, and also reveals the integrable structure of the problem. We
supplement this result by extending the familiar approach to the problem of the
Fermi Edge Singularity via the bosonic representation of the electronic
operators to non-equilibrium settings. It provides a compact way to extract the
leading asymptotes.Comment: Accepted for publication, J. Phys.
Pairing in High Temperature Superconductors and Berry Phase
The topological approach to the understanding of pairing mechanism in high
superconductors analyses the relevance of the Berry phase factor in this
context. This also gives the evidence for the pairing mechanism to be of
magnetic origin.Comment: 6 page
Hofstadter butterfly as Quantum phase diagram
The Hofstadter butterfly is viewed as a quantum phase diagram with infinitely
many phases, labelled by their (integer) Hall conductance, and a fractal
structure. We describe various properties of this phase diagram: We establish
Gibbs phase rules; count the number of components of each phase, and
characterize the set of multiple phase coexistence.Comment: 4 prl pages 1 colored figure typos corrected, reference [26] added,
"Ten Martini" assumption adde
Raman Scattering and Anomalous Current Algebra: Observation of Chiral Bound State in Mott Insulators
Recent experiments on inelastic light scattering in a number of insulating
cuprates [1] revealed a new excitation appearing in the case of crossed
polarizations just below the optical absorption threshold. This observation
suggests that there exists a local exciton-like state with an odd parity with
respect to a spatial reflection. We present the theory of high energy large
shift Raman scattering in Mott insulators and interpret the experiment [1] as
an evidence of a chiral bound state of a hole and a doubly occupied site with a
topological magnetic excitation. A formation of these composites is a crucial
feature of various topological mechanisms of superconductivity. We show that
inelastic light scattering provides an instrument for direct measurements of a
local chirality and anomalous terms in the electronic current algebra.Comment: 18 pages, TeX, C Version 3.
Tunneling and orthogonality catastrophe in the topological mechanism of superconductivity
We compute the angular dependence of the order parameter and tunneling
amplitude in a model exhibiting topological superconductivity and sketch its
derivation as a model of a doped Mott insulator. We show that ground states
differing by an odd number of particles are orthogonal and the order parameter
is in the d-representation, although the gap in the electronic spectrum has no
nodes. We also develop an operator algebra, that allowes one to compute
off-diagonal correlation functions.Comment: 4 pages, Revtex, psfig; some references are correcte
Magnetic properties of the Anderson model: a local moment approach
We develop a local moment approach to static properties of the symmetric
Anderson model in the presence of a magnetic field, focussing in particular on
the strong coupling Kondo regime. The approach is innately simple and
physically transparent; but is found to give good agreement, for essentially
all field strengths, with exact results for the Wilson ratio, impurity
magnetization, spin susceptibility and related properties.Comment: 7 pages, 3 postscript figues. Latex 2e using the epl.cls Europhysics
Letters macro packag
Chiral non-linear sigma-models as models for topological superconductivity
We study the mechanism of topological superconductivity in a hierarchical
chain of chiral non-linear sigma-models (models of current algebra) in one,
two, and three spatial dimensions. The models have roots in the 1D
Peierls-Frohlich model and illustrate how the 1D Frohlich's ideal conductivity
extends to a genuine superconductivity in dimensions higher than one. The
mechanism is based on the fact that a point-like topological soliton carries an
electric charge. We discuss a flux quantization mechanism and show that it is
essentially a generalization of the persistent current phenomenon, known in
quantum wires. We also discuss why the superconducting state is stable in the
presence of a weak disorder.Comment: 5 pages, revtex, no figure
Entanglement entropy and quantum phase transitions in quantum dots coupled to Luttinger liquid wires
We study a quantum phase transition which occurs in a system composed of two
impurities (or quantum dots) each coupled to a different interacting
(Luttinger-liquid) lead. While the impurities are coupled electrostatically,
there is no tunneling between them. Using a mapping of this system onto a Kondo
model, we show analytically that the system undergoes a
Berezinskii-Kosterlitz-Thouless quantum phase transition as function of the
Luttinger liquid parameter in the leads and the dot-lead interaction. The phase
with low values of the Luttinger-liquid parameter is characterized by an abrupt
switch of the population between the impurities as function of a common applied
gate voltage. However, this behavior is hard to verify numerically since one
would have to study extremely long systems. Interestingly though, at the
transition the entanglement entropy drops from a finite value of to
zero. The drop becomes sharp for infinite systems. One can employ finite size
scaling to extrapolate the transition point and the behavior in its vicinity
from the behavior of the entanglement entropy in moderate size samples. We
employ the density matrix renormalization group numerical procedure to
calculate the entanglement entropy of systems with lead lengths of up to 480
sites. Using finite size scaling we extract the transition value and show it to
be in good agreement with the analytical prediction.Comment: 12 pages, 9 figure
Tunneling in the topological mechanism of superconductivity
We compute the two-particle matrix element and Josephson tunneling amplitude
in a two-dimensional model of topological superconductivity which captures the
physics of the doped Mott insulator. The hydrodynamics of topological
electronic liquid consists of the compressible charge sector and the
incompressible chiral topological spin liquid. We show that ground states
differing by an odd number of particles are orthogonal and insertion of two
extra electrons is followed by the emission of soft modes of the transversal
spin current. The orthogonality catastrophe makes the physics of
superconductivity drastically different from the BCS-theory but similar to the
physics of one-dimensional electronic liquids. The wave function of a pair is
dressed by soft modes. As a result the two particle matrix element forms a
complex d-wave representation (i.e., changes sign under degree
rotation), although the gap in the electronic spectrum has no nodes. In
contrast to the BCS-theory the tunneling amplitude has an asymmetric broad peak
(much bigger than the gap) around the Fermi surface. We develop an operator
algebra, that allows one to compute other correlation functions.Comment: 18 pages, 2 eps figures, revtex, psfig, significant changes have been
mad
Orthogonality catastrophe and shock waves in a non-equilibrium Fermi gas
A semiclassical wave-packet propagating in a dissipationless Fermi gas
inevitably enters a "gradient catastrophe" regime, where an initially smooth
front develops large gradients and undergoes a dramatic shock wave phenomenon.
The non-linear effects in electronic transport are due to the curvature of the
electronic spectrum at the Fermi surface. They can be probed by a sudden
switching of a local potential. In equilibrium, this process produces a large
number of particle-hole pairs, a phenomenon closely related to the
Orthogonality Catastrophe. We study a generalization of this phenomenon to the
non-equilibrium regime and show how the Orthogonality Catastrophe cures the
Gradient Catastrophe, providing a dispersive regularization mechanism. We show
that a wave packet overturns and collapses into modulated oscillations with the
wave vector determined by the height of the initial wave. The oscillations
occupy a growing region extending forward with velocity proportional to the
initial height of the packet. We derive a fundamental equation for the
transition rates (MKP-equation) and solve it by means of the Whitham modulation
theory.Comment: 5 pages, 1 figure, revtex4, pr
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