636 research outputs found
Spin relaxation and combined resonance in two-dimensional electron systems with spin-orbit disorder
Disorder in spin-orbit (SO) coupling is an important feature of real
low-dimensional electron structures. We study spin relaxation due to such a
disorder as well as resulting abilities of spin manipulation. The spin
relaxation reveals quantum effects when the spatial scale of the randomness is
smaller than the electron wavelength. Due to the disorder in SO coupling, a
time-dependent external electric field generates a spatially random
spin-dependent perturbation. The resulting electric dipole spin resonance in a
two-dimensional electron gas leads to spin injection in a frequency range of
the order of the Fermi energy. These effects can be important for possible
applications in spintronics.Comment: 4 pages, 3 figure
Direct current driven by ac electric field in quantum wells
It is shown that the excitation of charge carriers by ac electric field with
zero average driving leads to a direct electric current in quantum well
structures. The current emerges for both linear and circular polarization of
the ac electric field and depends on the field polarization and frequency. We
present a micoscopic model and an analytical theory of such a nonlinear
electron transport in quantum wells with structure inversion asymmetry. In such
systems, dc current is induced by ac electric field which has both the in-plane
and out-of-plane components. The ac field polarized in the interface plane
gives rise to a direct current if the quantum well is subjected to an in-plane
static magnetic field.Comment: 6 pages, 3 figure
Spin-orbit Hanle effect in high-mobility quantum wells
We study the depolarization of optically oriented electrons in quantum wells
subjected to an in-plane magnetic field and show that the Hanle curve
drastically depends on the carrier mobility. In low-mobility structures, the
Hanle curve is described by a Lorentzian with the width determined by the
effective g-factor and the spin lifetime. In contrast, the magnetic field
dependence of spin polarization in high-mobility quantum wells is nonmonotonic:
The spin polarization rises with the magnetic field induction at small fields,
reaches maximum and then decreases. We show that the position of the Hanle
curve maximum can be used to directly measure the spin-orbit Rashba/Dresselhaus
magnetic field.Comment: 4 pages, 3 figure
Spin dephasing and pumping in graphene due to random spin-orbit interaction
We consider spin effects related to the random spin-orbit interaction in
graphene. Such a random interaction can result from the presence of ripples
and/or other inhomogeneities at the graphene surface. We show that the random
spin-orbit interaction generally reduces the spin dephasing (relaxation) time,
even if the interaction vanishes on average. Moreover, the random spin-orbit
coupling also allows for spin manipulation with an external electric field. Due
to the spin-flip interband as well as intraband optical transitions, the spin
density can be effectively generated by periodic electric field in a relatively
broad range of frequencies.Comment: 9 pages, 7 figure
Valley separation in graphene by polarized light
We show that the optical excitation of graphene with polarized light leads to
the pure valley current where carriers in the valleys counterflow. The current
in each valley originates from asymmetry of optical transitions and electron
scattering by impurities owing to the warping of electron energy spectrum. The
valley current has strong polarization dependence, its direction is opposite
for normally incident beams of orthogonal linear polarizations. In undoped
graphene on a substrate with high susceptibility, electron-electron scattering
leads to an additional contribution to the valley current that can dominate.Comment: 4+ pages, 2 figure
Self focusing mechanisms of an electron beam formed in a high voltage nanosecond low pressure discharge
On the nature of radiation of blue and green jets in laboratory discharges initiated by runaway electrons
Spectral and amplitude-temporal parameters of radiation from different regions of discharges initiated by runaway electrons have been studied. The pulse-periodic mode of discharge formation was used. It is shown that the color of a part of jets observed during laboratory discharges is determined by radiation of electrode metal vapors. It is found that blue mini jets from an electrode with a small radius of curvature appear in the cases of stainless steel and aluminum electrodes and are caused by emissions of atomic transitions of these metals. Green mini jets observed near copper electrodes are mainly caused by CuI atomic transitions mainly at wavelengths of 521.8 and 522 nm. It is confirmed that jets of different colors appear during formation of bright spots on electrodes, as well as sparks in the discharge
Tunneling spin-galvanic effect
It has been shown that tunneling of spin-polarized electrons through a
semiconductor barrier is accompanied by generation of an electric current in
the plane of the interfaces. The direction of this interface current is
determined by the spin orientation of the electrons, in particular the current
changes its direction if the spin orientation changes the sign. Microscopic
origin of such a 'tunneling spin-galvanic' effect is the spin-orbit
coupling-induced dependence of the barrier transparency on the spin orientation
and the wavevector of electrons.Comment: 3 pages, 2 figure
Dynamics of ionization processes in high-pressure nitrogen, air, and SF6 during a subnanosecond breakdown initiated by runaway electrons
The dynamics of ionization processes in high-pressure nitrogen, air, and SF6 during breakdown of a gap with a nonuniform distribution of the electric field by nanosecond high-voltage pulses was studied experimentally. Measurements of the amplitude and temporal characteristics of a diffuse discharge and its radiation with a subnanosecond time resolution have shown that, at any polarity of the electrode with a small curvature radius, breakdown of the gap occurs via two ionization waves, the first of which is initiated by runaway electrons. For a voltage pulse with an ∼500-ps front, UV radiation from different zones of a diffuse discharge is measured with a subnanosecond time resolution. It is shown that the propagation velocity of the first ionization wave increases after its front has passed one-half of the gap, as well as when the pressure in the discharge chamber is reduced and/or when SF6 is replaced with air or nitrogen. It is found that, at nitrogen pressures of 0.4 and 0.7 MPa and the positive polarity of the high-voltage electrode with a small curvature radius, the ionization wave forms with a larger (∼30 ps) time delay with respect to applying the voltage pulse to the gap than at the negative polarity. The velocity of the second ionization wave propagating from the plane electrode is measured. In a discharge in nitrogen at a pressure of 0.7 MPa, this velocity is found to be ∼10 cm/ns. It is shown that, as the nitrogen pressure increases to 0.7 MPa, the propagation velocity of the front of the first ionization wave at the positive polarity of the electrode with a small curvature radius becomes lower than that at the negative polarity
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