321 research outputs found
Spin magnetotransport in two-dimensional hole systems
Spin current of two-dimensional holes occupying the ground-state subband in
an asymmetric quantum well and interacting with static disorder potential is
calculated in the presence of a weak magnetic field H perpendicular to the well
plane. Both spin-orbit coupling and Zeeman coupling are taken into account. It
is shown that the applied electric field excites both the transverse
(spin-Hall) and diagonal spin currents, the latter changes its sign at a finite
H and becomes greater than the spin-Hall current as H increases. The effective
spin-Hall conductivity introduced to describe the spin response in Hall bars is
considerably enhanced by the magnetic field in the case of weak disorder and
demonstrates a non-monotonic dependence on H.Comment: 4 pages, 2 figures, published in Phys. Rev.
Frequency dependence of induced spin polarization and spin current in quantum wells
Dynamic response of two-dimensional electron systems with spin-orbit
interaction is studied theoretically on the basis of quantum kinetic equation,
taking into account elastic scattering of electrons. The spin polarization and
spin current induced by the applied electric field are calculated for the whole
class of electron systems described by p-linear spin-orbit Hamiltonians. The
absence of nonequilibrium intrinsic static spin currents is confirmed for these
systems with arbitrary (nonparabolic) electron energy spectrum. Relations
between the spin polarization, spin current, and electric current are
established. The general results are applied to the quantum wells grown in
[001] and [110] crystallographic directions, with both Rashba and Dresselhaus
types of spin-orbit coupling. It is shown that the existence of the fixed
(momentum-independent) precession axes in [001]-grown wells with equal Rashba
and Dresselhaus spin velocities or in symmetric [110]-grown wells leads to
vanishing spin polarizability at arbitrary frequency of the applied electric
field. This property is explained by the absence of Dyakonov-Perel-Kachorovskii
spin relaxation for the spins polarized along these precession axes. As a
result, a considerable frequency dispersion of spin polarization at very low
frequency in the vicinity of the fixed precession axes is predicted. Possible
effects of extrinsic spin-orbit coupling on the obtained results are discussed.Comment: 14 pages, 6 figures; published with minor corrections in Phys. Rev.
Suppression of spin-orbit effects in 1D system
We report the absence of spin effects such as spin-galvanic effect, spin
polarization and spin current under static electric field and
inter-spin-subband absorption in 1D system with spin-orbit interaction of
arbitrary form. It was also shown that the accounting for the direct
interaction of electron spin with magnetic field violates this statement.Comment: 8 pages, 1Figur
Spin diffusion/transport in -type GaAs quantum wells
The spin diffusion/transport in -type (001) GaAs quantum well at high
temperatures ( K) is studied by setting up and numerically solving the
kinetic spin Bloch equations together with the Poisson equation
self-consistently. All the scattering, especially the electron-electron Coulomb
scattering, is explicitly included and solved in the theory. This enables us to
study the system far away from the equilibrium, such as the hot-electron effect
induced by the external electric field parallel to the quantum well. We find
that the spin polarization/coherence oscillates along the transport direction
even when there is no external magnetic field. We show that when the scattering
is strong enough, electron spins with different momentums oscillate in the same
phase which leads to equal transversal spin injection length and ensemble
transversal injection length. It is also shown that the intrinsic scattering is
already strong enough for such a phenomena. The oscillation period is almost
independent on the external electric field which is in agreement with the
latest experiment in bulk system at very low temperature [Europhys. Lett. {\bf
75}, 597 (2006)]. The spin relaxation/dephasing along the diffusion/transport
can be well understood by the inhomogeneous broadening, which is caused by the
momentum-dependent diffusion and the spin-orbit coupling, and the scattering.
The scattering, temperature, quantum well width and external magnetic/electric
field dependence of the spin diffusion is studied in detail.Comment: 12 pages, 6 figures, to be published in J Appl. Phy
Andreev reflection and Klein tunneling in graphene
This is a colloquium-style introduction to two electronic processes in a
carbon monolayer (graphene), each having an analogue in relativistic quantum
mechanics. Both processes couple electron-like and hole-like states, through
the action of either a superconducting pair potential or an electrostatic
potential. The first process, Andreev reflection, is the electron-to-hole
conversion at the interface with a superconductor. The second process, Klein
tunneling, is the tunneling through a p-n junction. Existing and proposed
experiments on Josephson junctions and bipolar junctions in graphene are
discussed from a unified perspective.
CONTENTS:
I. INTRODUCTION
II. BASIC PHYSICS OF GRAPHENE (Dirac equation; Time reversal symmetry;
Boundary conditions; Pseudo-diffusive dynamics)
III. ANDREEV REFLECTION (Electron-hole conversion; Retro-reflection vs.
specular reflection; Dirac-Bogoliubov-de Gennes equation; Josephson junctions;
Further reading)
IV. KLEIN TUNNELING (Absence of backscattering; Bipolar junctions; Magnetic
field effects; Further reading)
V. ANALOGIES (Mapping between NS and p-n junction; Retro-reflection vs.
negative refraction; Valley-isospin dependent quantum Hall effect;
Pseudo-superconductivity)Comment: 20 pages, 28 figures; "Colloquium" for Reviews of Modern Physic
Hall resistance in the hopping regime, a "Hall Insulator"?
The Hall conductivity and resistivity of strongly localized electrons at low
temperatures and at small magnetic fields are obtained. It is found that the
results depend on whether the conductivity or the resistivity tensors are
averaged to obtain the macroscopic Hall resistivity. In the second case the
Hall resistivity always {\it diverges} exponentially as the temperature tends
to zero. But when the Hall resistivity is derived from the averaged
conductivity, the resulting temperature dependence is sensitive to the disorder
configuration. Then the Hall resistivity may approach a constant value as . This is the Hall insulating behavior. It is argued that for strictly dc
conditions, the transport quantity that should be averaged is the resistivity.Comment: Late
Randomly incomplete spectra and intermediate statistics
By randomly removing a fraction of levels from a given spectrum a model is
constructed that describes a crossover from this spectrum to a Poisson
spectrum. The formalism is applied to the transitions towards Poisson from
random matrix theory (RMT) spectra and picket fence spectra. It is shown that
the Fredholm determinant formalism of RMT extends naturally to describe
incomplete RMT spectra.Comment: 9 pages, 2 figures. To appear in Physical Review
Searching edges in the overlap of two plane graphs
Consider a pair of plane straight-line graphs, whose edges are colored red
and blue, respectively, and let n be the total complexity of both graphs. We
present a O(n log n)-time O(n)-space technique to preprocess such pair of
graphs, that enables efficient searches among the red-blue intersections along
edges of one of the graphs. Our technique has a number of applications to
geometric problems. This includes: (1) a solution to the batched red-blue
search problem [Dehne et al. 2006] in O(n log n) queries to the oracle; (2) an
algorithm to compute the maximum vertical distance between a pair of 3D
polyhedral terrains one of which is convex in O(n log n) time, where n is the
total complexity of both terrains; (3) an algorithm to construct the Hausdorff
Voronoi diagram of a family of point clusters in the plane in O((n+m) log^3 n)
time and O(n+m) space, where n is the total number of points in all clusters
and m is the number of crossings between all clusters; (4) an algorithm to
construct the farthest-color Voronoi diagram of the corners of n axis-aligned
rectangles in O(n log^2 n) time; (5) an algorithm to solve the stabbing circle
problem for n parallel line segments in the plane in optimal O(n log n) time.
All these results are new or improve on the best known algorithms.Comment: 22 pages, 6 figure
Lines pinning lines
A line g is a transversal to a family F of convex polytopes in 3-dimensional
space if it intersects every member of F. If, in addition, g is an isolated
point of the space of line transversals to F, we say that F is a pinning of g.
We show that any minimal pinning of a line by convex polytopes such that no
face of a polytope is coplanar with the line has size at most eight. If, in
addition, the polytopes are disjoint, then it has size at most six. We
completely characterize configurations of disjoint polytopes that form minimal
pinnings of a line.Comment: 27 pages, 10 figure
Voltage dependent conductance and shot noise in quantum microconstriction with single defects
The influence of the interference of electron waves, which are scattered by
single impurities and by a barrier on nonlinear conductance and shot noise of
metallic microconstriction is studied theoretically. It is shown that the these
characteristics are nonmonotonic functions on the applied bias.Comment: 18 pages,5 figure
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