1,109 research outputs found
Optical orientation of electron spins by linearly polarized light
Absorption of circularly polarized light in semiconductors is known to result
in optical orientation of electron and hole spins. It has been shown here that
in semiconductor quantum well structures spin orientation of carriers can be
achieved by linearly or even unpolarized light. Moreover, the sign and
magnitude of the spin orientation can be varied by rotating the polarization
plane of incidence light. The effect under study is related to reduced symmetry
of the quantum wells as compared to bulk materials and, microscopically, caused
by zero-field spin splitting of electron and hole states.Comment: 4 pages, 1 figur
Scattering induced spin orientation and spin currents in gyrotropic structures
It is shown that additional contributions both to current-induced spin
orientation and to the spin Hall effect arise in quantum wells due to gyrotropy
of the structures. Microscopically, they are related to basic properties of
gyrotropic systems, namely, linear in the wave vector terms in the matrix
element of electron scattering and in the energy spectrum. Calculation shows
that in high-mobility structures the contribution to the spin Hall current
considered here can exceed the term originated from the Mott skew scattering.Comment: 5 pages, 3 figure
Splitting of Resonant Frequencies of Acoustic Waves in Rotating Compressible Fluid
It is shown that in a rotating compressible fluid the resonant frequencies
(measured in a system of reference rotating together with the medium) for the
azimuthally running acoustic waves are split into two components. The received
results can be of practical significance as a basis of a method of measurements
of angular speed of medium and for acoustics of rotating technical devices.Comment: LaTeX file, 5 pages, 2 table
Spatiotemporal spin fluctuations caused by spin-orbit-coupled Brownian motion
We develop a theory of thermal fluctuations of spin density emerging in a
two-dimensional electron gas. The spin fluctuations probed at spatially
separated spots of the sample are correlated due to Brownian motion of
electrons and spin-obit coupling. We calculate the spatiotemporal correlation
functions of the spin density for both ballistic and diffusive transport of
electrons and analyze them for different types of spin-orbit interaction
including the isotropic Rashba model and persistent spin helix regime. The
measurement of spatial spin fluctuations provides direct access to the
parameters of spin-orbit coupling and spin transport in conditions close to the
thermal equilibrium.Comment: 5 pages, 4 figure
Electron spin dephasing in two-dimensional systems with anisotropic scattering
We develop a microscopic theory of spin relaxation of a two-dimensional
electron gas in quantum wells with anisotropic electron scattering. Both
precessional and collision-dominated regimes of spin dynamics are studied. It
is shown that, in quantum wells with noncentrosymmetric scatterers, the
in-plane and out-of-plane spin components are coupled: spin dephasing of
carriers initially polarized along the quantum well normal leads to the
emergence of an in-plane spin component even in the case of isotropic
spin-orbit splitting. In the collision-dominated regime, the
spin-relaxation-rate tensor is expressed in terms of the electric conductivity
tensor. We also study the effect of an in-plane and out-of-plane external
magnetic field on spin dephasing and show that the field dependence of electron
spin can be very intricate.Comment: 7 pages, 7 figure
Limitation of electron mobility from hyperfine interaction in ultra-clean quantum wells and topological insulators
The study of electron transport and scattering processes limiting electron
mobility in high-quality semiconductor structures is central to solid-state
electronics. Here, we uncover an unavoidable source of electron scattering
which is caused by fluctuations of nuclear spins. We calculate the momentum
relaxation time of electrons in quantum wells governed by the hyperfine
interaction between electrons and nuclei and show that this time drastically
depends on the spatial correlation of nuclear spins. Moreover, the scattering
processes accompanied by a spin flip are a source of the backscattering of
Dirac fermions at conducting surfaces of topological insulators.Comment: 5 page
Reflection of short polarized optical pulses from periodic and aperiodic multiple quantum well structures
We study the reflection of polarized optical pulses from resonant photonic
structures formed by periodic, Fibonacci, and gradient sequences of quantum
wells. The form and polarization of the reflected pulse are shown to be
determined by the structure design and optical length. In structures with
periodic quantum well arrangement, the response to ultrashort pulse is an
optical signal with a sharp rise followed by an exponential decay or Bessel
beats depending on the structure length. The duration of reflected pulses
non-monotonically depends on the number of quantum wells reaching the minimum
for a certain structure length which corresponds to the transition from
superradiant to photonic-crystalline regime. We also study the conversion of
pulse polarization in the longitudinal external magnetic field which splits the
exciton resonance. Comparing periodic, Fibonacci, and gradient structures we
show that the latter are more efficient for the conversion from linear to
circular polarization.Comment: 11 pages, 9 figure
Spring Changeover of the Middle Atmosphere Circulation Compared with Rocket Wind Data up to 80 Km
The middle atmosphere circulation is governed by two seasonal basic states in winter and summer, twice a year separated by relatively shortlived reversal periods. These seasonal basic states of circulation and the spring changeover period between them are investigated
Magnetic field effects on edge and bulk states in topological insulators based on HgTe/CdHgTe quantum wells with strong natural interface inversion asymmetry
We present a theory of the electron structure and the Zeeman effect for the
helical edge states emerging in two-dimensional topological insulators based on
HgTe/HgCdTe quantum wells with strong natural interface inversion asymmetry.
The interface inversion asymmetry, reflecting the real atomistic structure of
the quantum well, drastically modifies both bulk and edge states. For the
in-plane magnetic field, this asymmetry leads to a strong anisotropy of the
edge-state effective -factor which becomes dependent on the edge
orientation. The interface inversion asymmetry also couples the counter
propagating edge states in the out-of-plane magnetic field leading to the
opening of the gap in the edge-state spectrum by arbitrary small fields.Comment: 10 pages, 9 figure
Ratchet transport of a two-dimensional electron gas at cyclotron resonance
The driving of charge carriers confined in a quantum well lacking the center
of space inversion by an alternating electric field leads to the formation of a
direct electric current. We develop a microscopic theory of such a quantum
ratchet effect for quantum wells subjected to a static magnetic field. We show
that the ratchet current emerges for a linearly polarized alternating electric
field as well as a rotating electric field and drastically increases at the
cyclotron resonance conditions. For the magnetic field tilted with respect to
the quantum well normal, the ratchet current contains an additional resonance
at the first subharmonic of the cyclotron resonance.Comment: 8 pages, 4 figure
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