507 research outputs found
Observing the spin-Coulomb drag in spin-valve devices
The Coulomb interaction between electrons of opposite spin orientations in a
metal or in a doped semiconductor results in a negative off-diagonal component
of the electrical resistivity matrix -- the so-called "spin-drag resistivity".
It is generally quite difficult to separate the spin-drag contribution from
more conventional mechanisms of resistivity. In this paper I discuss two
methods to accomplish this separation in a spin-valve device.Comment: 11 pages, 5 figure
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
Spin Coulomb drag beyond the random phase approximation
We study the spin Coulomb drag in a quasi-two-dimensional electron gas beyond
the random phase approximation (RPA). We find that the finite transverse width
of the electron gas causes a significant reduction of the spin Coulomb drag.
This reduction, however, is largely compensated by the enhancement coming from
the inclusion of many-body local field effects beyond the RPA, thereby
restoring good agreement with the experimental observations by C. P. Weber
\textit{et al.}, Nature, \textbf{437}, 1330 (2005).Comment: 3 figures, accepted for publication in Phys. Rev. Let
Electronic viscosity in a quantum well: A test for the local density approximation
In the local density approximation (LDA) for electronic time-dependent
current-density functional theory (TDCDFT) many-body effects are described in
terms of the visco-elastic constants of the homogeneous three-dimensional
electron gas. In this paper we critically examine the applicability of the
three-dimensional LDA to the calculation of the viscous damping of
1-dimensional collective oscillations of angular frequency in a quasi
2-dimensional quantum well. We calculate the effective viscosity
from perturbation theory in the screened Coulomb interaction
and compare it with the commonly used three-dimensional LDA viscosity
. Significant differences are found. At low frequency is
dominated by a shear term, which is absent in . At high
frequency and exhibit different power law behaviors
( and respectively), reflecting different spectral
densities of electron-hole excitations in two and three dimensions. These
findings demonstrate the need for better approximations for the
exchange-correlation stress tensor in specific systems where the use of the
three-dimensional functionals may lead to unphysical results.Comment: 10 pages, 7 figures, RevTex
Bosonization of the two-dimensional electron gas in the lowest Landau level
We develop a bosonization scheme for the collective dynamics of a spinless
two-dimensional electron gas (2DEG) in the lowest Landau level. The system is
treated as a continuous elastic medium, and quantum commutation relations are
imposed between orthogonal components of the elastic displacement field. This
theory provides a unified description of bulk and edge excitations of
compressible and incompressible phases, and explains the results of recent
tunneling experiments at the edge of the 2DEG.Comment: 4 pages, includes 1 figur
Violation of the Wiedemann-Franz law in clean graphene layers
The Wiedemann-Franz law, connecting the electronic thermal conductivity to
the electrical conductivity of a disordered metal, is generally found to be
well satisfied even when electron-electron (e-e) interactions are strong. In
ultra-clean conductors, however, large deviations from the standard form of the
law are expected, due to the fact that e-e interactions affect the two
conductivities in radically different ways. Thus, the standard Wiedemann-Franz
ratio between the thermal and the electric conductivity is reduced by a factor
, where is the momentum relaxation
rate, and is the relaxation time of the thermal
current due to e-e collisions. Here we study the density and temperature
dependence of in the important case of doped, clean
single layers of graphene, which exhibit record-high thermal conductivities. We
show that at low temperature is of the
quasiparticle decay rate. We also show that the many-body renormalization of
the thermal Drude weight coincides with that of the Fermi velocity.Comment: 6 pages, 5 appendices (13 pages
On the "Causality Paradox" of Time-Dependent Density Functional Theory
I show that the so-called causality paradox of time-dependent density
functional theory arises from an incorrect formulation of the variational
principle for the time evolution of the density. The correct formulation not
only resolves the paradox in real time, but also leads to a new expression for
the causal exchange-correlation kernel in terms of Berry curvature.
Furthermore, I show that all the results that were previously derived from
symmetries of the action functional remain valid in the present formulation.
Finally, I develop a model functional theory which explicitly demonstrates the
workings of the new formulation.Comment: 21 page
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