9,357 research outputs found
Electron spin relaxation in cubic GaN quantum dots
The spin relaxation time in zinc blende GaN quantum dot is
investigated for different magnetic field, well width and quantum dot diameter.
The spin relaxation caused by the two most important spin relaxation mechanisms
in zinc blende semiconductor quantum dots, {i.e.} the electron-phonon
scattering in conjunction with the Dresselhaus spin-orbit coupling and the
second-order process of the hyperfine interaction combined with the
electron-phonon scattering, are systematically studied. The relative importance
of the two mechanisms are compared in detail under different conditions. It is
found that due to the small spin orbit coupling in GaN, the spin relaxation
caused by the second-order process of the hyperfine interaction combined with
the electron-phonon scattering plays much more important role than it does in
the quantum dot with narrower band gap and larger spin-orbit coupling, such as
GaAs and InAs.Comment: 8 pages, 5 figures, PRB 79, 2009, in pres
Spin-roton excitations in the cuprate superconductors
We identify a new kind of elementary excitations, spin-rotons, in the doped
Mott insulator. They play a central role in deciding the superconducting
transition temperature Tc, resulting in a simple Tc formula,Tc=Eg/6, with Eg as
the characteristic energy scale of the spin rotons. We show that the degenerate
S=1 and S=0 rotons can be probed by neutron scattering and Raman scattering
measurements, respectively, in good agreement with the magnetic resonancelike
mode and the Raman A1g mode observed in the high-Tc cuprates.Comment: 10 pages, 9 figure
Measurements of the effect of horizontal variability of atmospheric backscatter on dial measurements
The horizontal variability of atmospheric backscatter may have a substantial effect on how Differential Absorption Lidar (DIAL) data must be taken and analyzed. To minimize errors, lidar pulse pairs are taken with time separations which are short compared to the time scales associated with variations in atmospheric backscatter. To assess the atmospheric variability for time scales which are long compared to the lidar pulse repetition rate, the variance of the lidar return signal in a given channel can be computed. The variances of the on-line, off-line, and ration of the on-line to off-line signals at given altitudes obtained with the dual solid-state Alexandrite laser system were calculated. These evaluations were made for both down-looking aircraft and up-looking ground-based lidar data. Data were taken with 200 microsecond separation between on-line and off-line laser pulses, 30 m altitude resolution, 5 Hz repetition rate, and the signal were normalized for outgoing laser energy
Quantum Spin Hall Effect and Topologically Invariant Chern Numbers
We present a topological description of quantum spin Hall effect (QSHE) in a
two-dimensional electron system on honeycomb lattice with both intrinsic and
Rashba spin-orbit couplings. We show that the topology of the band insulator
can be characterized by a traceless matrix of first Chern integers.
The nontrivial QSHE phase is identified by the nonzero diagonal matrix elements
of the Chern number matrix (CNM). A spin Chern number is derived from the CNM,
which is conserved in the presence of finite disorder scattering and spin
nonconserving Rashba coupling. By using the Laughlin's gedanken experiment, we
numerically calculate the spin polarization and spin transfer rate of the
conducting edge states, and determine a phase diagram for the QSHE.Comment: 4 pages and 4 figure
-valley electron factor in bulk GaAs and AlAs
We study the Land\'e -factor of conduction electrons in the -valley of
bulk GaAs and AlAs by using a three-band model
together with the tight-binding model. We find that the -valley -factor
is highly anisotropic, and can be characterized by two components,
and . is close to the free electron Land\'e factor but
is strongly affected by the remote bands. The contribution from remote
bands on depends on how the remote bands are treated. However, when
the magnetic field is in the Voigt configuration, which is widely used in the
experiments, different models give almost identical -factor.Comment: 4 pages, 1 figure, To be published in J. App. Phys. 104, 200
Spin Hall Effect and Spin Transfer in Disordered Rashba Model
Based on numerical study of the Rashba model, we show that the spin Hall
conductance remains finite in the presence of disorder up to a characteristic
length scale, beyond which it vanishes exponentially with the system size. We
further perform a Laughlin's gauge experiment numerically and find that all
energy levels cannot cross each other during an adiabatic insertion of the flux
in accordance with the general level-repulsion rule. It results in zero spin
transfer between two edges of the sample as each state always evolves back
after the insertion of one flux quantum, in contrast to the quantum Hall
effect. It implies that the topological spin Hall effect vanishes with the
turn-on of disorder.Comment: 4 pages, 4 figures final versio
Magnetic Incommensurability in Doped Mott Insulator
In this paper we explore the incommensurate spatial modulation of spin-spin
correlations as the intrinsic property of the doped Mott insulator, described
by the model. We show that such an incommensurability is a direct
manifestation of the phase string effect introduced by doped holes in both one-
and two-dimensional cases. The magnetic incommensurate peaks of dynamic spin
susceptibility in momentum space are in agreement with the neutron-scattering
measurement of cuprate superconductors in both position and doping dependence.
In particular, this incommensurate structure can naturally reconcile the
neutron-scattering and NMR experiments of cuprates.Comment: 12 pages (RevTex), five postscript figure
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