541 research outputs found
Coulomb Drag and Spin Coulomb Drag in the presence of Spin-orbit Coupling
Employing diagrammatic perturbation theory, we calculate the (charge) Coulomb
drag resistivity and spin Coulomb drag resistivity
in the presence of Rashba spin-orbit coupling.
Analytical expressions for and are
derived, and it is found that spin-orbit interaction produces a small
enhancement to and in the ballistic regime
while is unchanged in the diffusive regime. This enhancement in the
ballistic regime is attributed to the enhancement of the nonlinear
susceptibility (i.e. current produced through the rectification of the thermal
electric potential fluctuations in the passive layer) while the lack of
enhancement in the diffusive regime is due to the suppression by disorder.Comment: 8 pages, 2 figure
Magneto-optical and Magneto-electric Effects of Topological Insulators in Quantizing Magnetic Fields
We develop a theory of the magneto-optical and magneto-electric properties of
a topological insulator thin film in the presence of a quantizing external
magnetic field. We find that low-frequency magneto-optical properties depend
only on the sum of top and bottom surface Dirac-cone filling factors
and , whereas the low-frequency
magneto-electric response depends only on the difference. The Faraday rotation
is quantized in integer multiples of the fine structure constant and the Kerr
effect exhibits a rotation. Strongly enhanced cyclotron-resonance
features appear at higher frequencies that are sensitive to the filling factors
of both surfaces. When the product of the bulk conductivity and the film
thickness in units is small compared to , magneto-optical
properties are only weakly dependent on accidental doping in the interior of
the film.Comment: 4 page
Giant Magneto-optical Kerr Effect and Universal Faraday Effect in Thin-film Topological Insulators
Topological insulators can exhibit strong magnetoelectric effects when their
time-reversal symmetry is broken. In this Letter we consider the
magneto-optical Kerr and Faraday effects of a topological insulator thin film
weakly exchange-coupled to a ferromagnet. We find that its Faraday rotation has
a universal value at low-frequencies, where is the vacuum fine structure
constant, and that it has a giant Kerr rotation .
These properties follow from a delicate interplay between thin-film cavity
confinement and the surface Hall conductivity of a topological insulator's
helical quasiparticles.Comment: 5 pages, 4 figure
Energy Relaxation of Hot Dirac Fermions in Graphene
We develop a theory for the energy relaxation of hot Dirac fermions in
graphene. We obtain a generic expression for the energy relaxation rate due to
electron-phonon interaction and calculate the power loss due to both optical
and acoustic phonon emission as a function of electron temperature
and density . We find an intrinsic power loss weakly
dependent on carrier density and non-vanishing at the Dirac point ,
originating from interband electron-optical phonon scattering by the intrinsic
electrons in the graphene valence band. We obtain the total power loss per
carrier within the range of electron
temperatures . We find optical (acoustic) phonon
emission to dominate the energy loss for in the density range .Comment: 5 page
Ballistic Hot Electron Transport in Graphene
We theoretically study the inelastic scattering rate and the carrier mean
free path for energetic hot electrons in graphene, including both
electron-electron and electron-phonon interactions. Taking account of optical
phonon emission and electron-electron scattering, we find that the inelastic
scattering time and the mean free path
for electron densities . In particular, we find that the mean free path exhibits a
finite jump at the phonon energy due to electron-phonon
interaction. Our results are directly applicable to device structures where
ballistic transport is relevant with inelastic scattering dominating over
elastic scattering.Comment: 4 page
Spin Accumulation in the Extrinsic Spin Hall Effect
The drift-diffusion formalism for spin-polarized carrier transport in
semiconductors is generalized to include spin-orbit coupling. The theory is
applied to treat the extrinsic spin Hall effect using realistic boundary
conditions. It is shown that carrier and spin diffusion lengths are modified by
the presence of spin-orbit coupling and that spin accumulation due to the
extrinsic spin Hall effect is strongly and qualitatively influenced by boundary
conditions. Analytical formulas for the spin-dependent carrier recombination
rates and inhomogeneous spin densities and currents are presented.Comment: 5 pages, 3 figure
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