2,769 research outputs found
Coherent transport in disordered metals out of equilibrium
We derive a formula for the quantum corrections to the electrical current for
a metal out of equilibrium. In the limit of linear current-voltage
characteristics our formula reproduces the well known Altshuler-Aronov
correction to the conductivity of a disordered metal. The current formula is
obtained by a direct diagrammatic approach, and is shown to agree with what is
obtained within the Keldysh formulation of the non-linear sigma model. As an
application we calculate the current of a mesoscopic wire. We find a
current-voltage characteristics that scales with , and calculate the
different scaling curves for a wire in the hot-electron regime and in the
regime of full non-equilibrium.Comment: 16 pages, 13 figure
Coherent transport in disordered metals: zero dimensional limit
We consider non-equilibrium transport in disordered conductors. We calculate
the interaction correction to the current for a short wire connected to
electron reservoirs by resistive interfaces. In the absence of charging effects
we find a universal current-voltage-characteristics. The relevance of our
calculation for existing experiments is discussed as well as the connection
with alternative theoretical approaches
Quasiclassical theory of charge transport in disordered interacting electron systems
We consider the corrections to the Boltzmann theory of electrical transport
arising from the Coulomb interaction in disordered conductors. In this article
the theory is formulated in terms of quasiclassical Green's functions. We
demonstrate that the formalism is equivalent to the conventional diagrammatic
technique by deriving the well-known Altshuler-Aronov corrections to the
conductivity. Compared to the conventional approach, the quasiclassical theory
has the advantage of being closer to the Boltzmann theory, and also allows
description of interaction effects in the transport across interfaces, as well
as non-equilibrium phenomena in the same theoretical framework. As an example,
by applying the Zaitsev boundary conditions which were originally developed for
superconductors, we obtain the -theory of the Coulomb blockade in tunnel
junctions. Furthermore we summarize recent results obtained for the
non-equilibrium transport in thin films, wires and fully coherent conductors.Comment: 46 pages; review articl
Spin current swapping and Hanle spin Hall effect in the two dimensional electron gas
We analyze the effect known as "spin current swapping" (SCS) due to
electron-impurity scattering in a uniform spin-polarized two-dimensional
electron gas. In this effect a primary spin current (lower index for
spatial direction, upper index for spin direction) generates a secondary spin
current if , or , with , if . Contrary
to naive expectation, the homogeneous spin current associated with the uniform
drift of the spin polarization in the electron gas does not generate a swapped
spin current by the SCS mechanism. Nevertheless, a swapped spin current will be
generated, if a magnetic field is present, by a completely different mechanism,
namely, the precession of the spin Hall spin current in the magnetic field. We
refer to this second mechanism as Hanle spin Hall effect, and we notice that it
can be observed in an experiment in which a homogeneous drift current is passed
through a uniformly magnetized electron gas. In contrast to this, we show that
an unambiguous observation of SCS requires inhomogeneous spin currents, such as
those that are associated with spin diffusion in a metal, and no magnetic
field. An experimental setup for the observation of the SCS is therefore
proposed.Comment: 8 pages, 5 figure
Onsager relations in a two-dimensional electron gas with spin-orbit coupling
Theory predicts for the two-dimensional electrons gas with only Rashba
spin-orbit interaction a vanishing spin Hall conductivity and at the same time
a finite inverse spin Hall effect. We show how these seemingly contradictory
results are compatible with the Onsager relations: the latter do hold for spin
and particle (charge) currents in the two-dimensional electron gas, although
(i) their form depends on the experimental setup and (ii) a vanishing bulk spin
Hall conductivity does not necessarily imply a vanishing spin Hall effect. We
also discuss the situation in which extrinsic spin orbit from impurities is
present and the bulk spin Hall conductivity can be different from zero.Comment: Accepted versio
Spin thermoelectrics in a disordered Fermi gas
We study the connection between the spin-heat and spin-charge response in a
disordered Fermi gas with spin-orbit coupling. It is shown that the ratio
between the above responses can be expressed as the thermopower times a number which depends on the strength and
type of the spin-orbit couplings considered. The general results are
illustrated by examining different two-dimensional electron or hole systems
with different and competing spin-orbit mechanisms, and we conclude that a
metallic system could prove much more efficient as a heat-to-spin than as a
heat-to-charge converter.Comment: 6 pages, 1 figur
Renormalization group and Ward identities in quantum liquid phases and in unconventional critical phenomena
By reviewing the application of the renormalization group to different
theoretical problems, we emphasize the role played by the general symmetry
properties in identifying the relevant running variables describing the
behavior of a given physical system. In particular, we show how the constraints
due to the Ward identities, which implement the conservation laws associated
with the various symmetries, help to minimize the number of independent running
variables. This use of the Ward identities is examined both in the case of a
stable phase and of a critical phenomenon. In the first case we consider the
problems of interacting fermions and bosons. In one dimension general and
specific Ward identities are sufficient to show the non-Fermi-liquid character
of the interacting fermion system, and also allow to describe the crossover to
a Fermi liquid above one dimension. This crossover is examined both in the
absence and presence of singular interaction. On the other hand, in the case of
interacting bosons in the superfluid phase, the implementation of the Ward
identities provides the asymptotically exact description of the acoustic
low-energy excitation spectrum, and clarifies the subtle mechanism of how this
is realized below and above three dimensions. As a critical phenomenon, we
discuss the disorder-driven metal-insulator transition in a disordered
interacting Fermi system. In this case, through the use of Ward identities, one
is able to associate all the disorder effects to renormalizations of the Landau
parameters. As a consequence, the occurrence of a metal-insulator transition is
described as a critical breakdown of a Fermi liquid.Comment: 47 pages, 11 figure
Spin Hall and Edelstein effects in metallic films: from 2D to 3D
A normal metallic film sandwiched between two insulators may have strong
spin-orbit coupling near the metal-insulator interfaces, even if spin-orbit
coupling is negligible in the bulk of the film. In this paper we study two
technologically important and deeply interconnected effects that arise from
interfacial spin-orbit coupling in metallic films. The first is the spin Hall
effect, whereby a charge current in the plane of the film is partially
converted into an orthogonal spin current in the same plane. The second is the
Edelstein effect, in which a charge current produces an in-plane, transverse
spin polarization. At variance with strictly two-dimensional Rashba systems, we
find that the spin Hall conductivity has a finite value even if spin-orbit
interaction with impurities is neglected and "vertex corrections" are properly
taken into account. Even more remarkably, such finite value becomes "universal"
in a certain configuration. This is a direct consequence of the spatial
dependence of spin-orbit coupling on the third dimension, perpendicular to the
film plane. The non-vanishing spin Hall conductivity has a profound influence
on the Edelstein effect, which we show to consist of two terms, the first with
the standard form valid in a strictly two-dimensional Rashba system, and a
second arising from the presence of the third dimension. Whereas the standard
term is proportional to the momentum relaxation time, the new one scales with
the spin relaxation time. Our results, although derived in a specific model,
should be valid rather generally, whenever a spatially dependent Rashba
spin-orbit coupling is present and the electron motion is not strictly
two-dimensional.Comment: 23 pages, 3 figure
Non-linear conductivity and quantum interference in disordered metals
We report on a novel non-linear electric field effect in the conductivity of
disordered conductors. We find that an electric field gives rise to dephasing
in the particle-hole channel, which depresses the interference effects due to
disorder and interaction and leads to a non-linear conductivity. This
non-linear effect introduces a field dependent temperature scale and
provides a microscopic mechanism for electric field scaling at the
metal-insulator transition. We also study the magnetic field dependence of the
non-linear conductivity and suggest possible ways to experimentally verify our
predictions. These effects offer a new probe to test the role of quantum
interference at the metal-insulator transition in disordered conductors.Comment: 5 pages, 3 figure
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