7,894 research outputs found
Spin current injection by intersubband transitions in quantum wells
We show that a pure spin current can be injected in quantum wells by the
absorption of linearly polarized infrared radiation, leading to transitions
between subbands. The magnitude and the direction of the spin current depend on
the Dresselhaus and Rashba spin-orbit coupling constants and light frequency
and, therefore, can be manipulated by changing the light frequency and/or
applying an external bias across the quantum well. The injected spin current
should be observable either as a voltage generated via the anomalous spin-Hall
effect, or by spatially resolved pump-probe optical spectroscopy.Comment: minor changes, short version publishe
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
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
Physical Limits of the ballistic and non-ballistic Spin-Field-Effect Transistor: Spin Dynamics in Remote Doped Structures
We investigate the spin dynamics and relaxation in remotely-doped two
dimensional electron systems where the dopants lead to random fluctuations of
the Rashba spin-orbit coupling. Due to the resulting random spin precession,
the spin relaxation time is limited by the strength and spatial scale of the
random contribution to the spin-orbit coupling. We concentrate on the role of
the randomness for two systems where the direction of the spin-orbit field does
not depend on the electron momentum: the spin field-effect transistor with
balanced Rashba and Dresselhaus couplings and the (011) quantum well. Both of
these systems are considered as promising for the spintronics applications
because of the suppression of the Dyakonov-Perel' mechanism there makes the
realization of a spin field effect transistor in the diffusive regime possible.
We demonstrate that the spin relaxation through the randomness of spin-orbit
coupling imposes important physical limitations on the operational properties
of these devices.Comment: 10 pages, 4 figure
Coherent spin dynamics in quantum wells in quantizing magnetic field
We investigate theoretically the coherent longitudinal and transversal spin
relaxation of photoexcited electrons in quantum wells in quantized magnetic
fields. We find the relaxation time for typical quantum well parameters between
100 and 1000 ps. For a realistic random potential the relaxation process
depends on the electron energy and g-factor, demonstrating oscillations in the
spin polarization accompanying the spin relaxation. The dependence of spin
relaxation on applied field, and thus on the corresponding "magnetic" length,
can be used to characterize the spatial scale of disorder in quantum wells.Comment: 13 pages, 4 figure
Quasiparticle states of the Hubbard model near the Fermi level
The spectra of the t-U and t-t'-U Hubbard models are investigated in the
one-loop approximation for different values of the electron filling. It is
shown that the four-band structure which is inherent in the case of
half-filling and low temperatures persists also for some excess or deficiency
of electrons. Besides, with some departure from half-filling an additional
narrow band of quasiparticle states arises near the Fermi level. The dispersion
of the band, its bandwidth and the variation with filling are close to those of
the spin-polaron band of the t-J model. For moderate doping spectral
intensities in the new band and in one of the inner bands of the four-band
structure decrease as the Fermi level is approached which leads to the
appearance of a pseudogap in the spectrum.Comment: 8 pages, 7 figure
The effects of disorder in dimerized quantum magnets in mean field approximations
We study theoretically the effects of disorder on Bose-Einstein condensates
(BEC) of bosonic triplon quasiparticles in doped dimerized quantum magnets. The
condensation occurs in a strong enough magnetic field Hc, where the
concentration of bosons in the random potential is sufficient to form the
condensate. The effect of doping is partly modeled by delta - correlated
disorder potential, which (i) leads to the uniform renormalization of the
system parameters and (ii) produces disorder in the system with renormalized
parameters. These approaches can explain qualitatively the available
magnetization data in the Tl_(1-x)K_(x)CuCl_3 compound taken as an example. In
addition to the magnetization, we found that the speed of the Bogoliubov mode
has a peak as a function of doping parameter, x. No evidence of the pure Bose
glass phase has been obtained in the BEC regime.Comment: Includes 19 pages, 5 figure
Solar radiation on Mars: Stationary photovoltaic array
Solar energy is likely to be an important power source for surface-based operation on Mars. Photovoltaic cells offer many advantages. In this article we have presented analytical expressions and solar radiation data for stationary flat surfaces (horizontal and inclined) as a function of latitude, season and atmospheric dust load (optical depth). The diffuse component of the solar radiation on Mars can be significant, thus greatly affecting the optimal inclination angle of the photovoltaic surface
Robust to impurity-scattering spin Hall effect in two-dimensional electron gas
We propose a mechanism of spin Hall effect in two-dimensional electron gas
with spatially random Rashba spin-orbit interaction. The calculations based on
the Kubo formalism and kinetic equation show that in contrast to the constant
spin-orbit coupling, spin Hall conductivity in the random spin-orbit field is
not totally suppressed by the potential impurity scattering. Even if the
regular contribution is removed by the vertex corrections, the terms we
consider, remain. Therefore, the intrinsic spin-Hall effect exists being,
however, non-universal.Comment: 4+ pages, 2 figure
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