297 research outputs found
Equilibrium Current and Orbital Magnetization in a Quantum Hall Fluid
We present a general theory for the equilibrium current distribution in an
interacting two-dimensional electron gas subjected to a perpendicular magnetic
field, and confined by a potential that varies slowly on the scale of the
magnetic length. The distribution is found to consist of strips or channels of
current, which alternate in direction, and which have universal integrated
strength.Comment: 13 pages, Revtex, to appear in the proceedings of the "Workshop on
Novel Physics in Low-Dimensional Electron Systems" held in Madra
Quantum Breathing Mode for Electrons with 1/r^2 Interaction
We discuss a collective "breathing" mode of electrons with inverse-square-law
interactions in a two-dimensional quantum dot and a perpendicular magnetic
field.Comment: 1 page, Revtex, submitted to "Comment" Section of Phys. Rev. Let
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
Comment on "Modifying the variational principle in the action integral functional derivation of time-dependent density functional theory" by Jochen Schirmer [arXiv:1010.4223]
In a paper recently published in Phys. Rev. A [arXiv:1010.4223], Schirmer has
criticized an earlier work of mine [arXiv:0803.2727], as well as the
foundations of time-dependent density functional theory. In Ref.[2], I showed
that the so-called "causality paradox" - i.e., the failure of the
exchange-correlation potential derived from the Runge-Gross time-dependent
variational principle to satisfy causality requirements - can be solved by a
careful reformulation of that variational principle. Fortunately, the criticism
presented in Ref.[1] is based on elementary misunderstandings of the nature of
functionals, gauge transformations, and the time-dependent variational
principle. In this Comment I wish to point out and clear these
misunderstandings.Comment: 4 pages. Accepted for publication in Phys. Rev.
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
Bound on the Group Velocity of an Electron in a 1D Periodic Potential
By using a recently derived upper bound on the allowed equilibrium current in
a ring, it is proved that the magnitude of the group velocity of a Bloch
electron in a one-dimensional periodic potential is always less than or equal
to the group velocity of the same Bloch state in an empty lattice. Our
inequality also implies that each energy band in a one-dimensional crystal
always lies below the corresponding free-electron band, when the minima of
those bands are aligned.Comment: 6 pages in Te
Universal Equilibrium Currents in the Quantum Hall Fluid
The equilibrium current distribution in a quantum Hall fluid that is
subjected to a slowly varying confining potential is shown to generally consist
of strips or channels of current, which alternate in direction, and which have
universal integrated strengths. A measurement of these currents would yield
direct independent measurements of the proper quasiparticle and quasihole
energies in the fractional quantum Hall states.Comment: 4 pages, Revte
Exact exchange-correlation potential for a time-dependent two electron system
We obtain an exact solution of the time-dependent Schroedinger equation for a
two-electron system confined to a plane by an isotropic parabolic potential
whose curvature is periodically modulated in time. From this solution we
compute the exact time-dependent exchange correlation potential v_xc which
enters the Kohn-Sham equation of time-dependent density functional theory. Our
exact result provides a benchmark against which various approximate forms for
v_xc can be compared. Finally v_xc is separated in an adiabatic and a pure
dynamical part and it is shown that, for the particular system studied, the
dynamical part is negligible.Comment: 23 pages, 6 figure
Spin drag in an ultracold Fermi gas on the verge of a ferromagnetic instability
Recent experiments [Jo et al., Science 325, 1521 (2009)] have presented
evidence of ferromagnetic correlations in a two-component ultracold Fermi gas
with strong repulsive interactions. Motivated by these experiments we consider
spin drag, i.e., frictional drag due to scattering of particles with opposite
spin, in such systems. We show that when the ferromagnetic state is approached
from the normal side, the spin drag relaxation rate is strongly enhanced near
the critical point. We also determine the temperature dependence of the spin
diffusion constant. In a trapped gas the spin drag relaxation rate determines
the damping of the spin dipole mode, which therefore provides a precursor
signal of the ferromagnetic phase transition that may be used to experimentally
determine the proximity to the ferromagnetic phase.Comment: 4 pages, 3 fig
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