46 research outputs found
Magnetic field effects on spin relaxation in heterostructures
Effect of magnetic field on electron spin relaxation in quantum wells is
studied theoretically. We have shown that Larmor effect and cyclotron motion of
carriers can either jointly suppress D'yakonov-Perel' spin relaxation or
compensate each other. The spin relaxation rates tensor is derived for any
given direction of the external field and arbitrary ratio of bulk and
structural contributions to spin splitting. Our results are applied to the
experiments on electron spin resonance in SiGe heterostructures, and enable us
to extract spin splitting value for such quantum wells.Comment: 6 pages, 4 figure
Introduction to spin physics in semiconductors
This lecture presents a brief survey of spin physics in semiconductors together with the historic roots of the recent activity in investigating spin-related phenomena
Spin relaxation and antisymmetric exchange in n-doped III-V semiconductor
Recently K. Kavokin [Phys. Rev. B 64, 075305 (2001)] suggested that the
Dzyaloshinskii-Moriya interaction between localized electrons governs slow spin
relaxation in -doped GaAs in the regime close to the metal-insulator
transition. We derive the correct spin Hamiltonian and apply it to the
determination of spin dephasing time using the method of moments expansion. We
argue that the proposed mechanism is insufficient to explain the observed
values of the spin relaxation time.Comment: 5 pages, 1 figure
Low-temperature spin relaxation in n-type GaAs
Low-temperature electron spin relaxation is studied by the optical
orientation method in bulk n-GaAs with donor concentrations from 10^14 cm^{-3}
to 5x10^17 cm^{-3}.
A peculiarity related to the metal-to-insulator transition (MIT) is observed
in the dependence of the spin lifetime on doping near n_D = 2x10^16 cm^{-3}. In
the metallic phase, spin relaxation is governed by the Dyakonov-Perel
mechanism, while in the insulator phase it is due to anisotropic exchange
interaction and hyperfine interactio
Anisotropic exchange interaction of localized conduction-band electrons in semiconductor structures
The spin-orbit interaction in semiconductors is shown to result in an
anisotropic contribution into the exchange Hamiltonian of a pair of localized
conduction-band electrons. The anisotropic exchange interaction exists in
semiconductor structures which are not symmetric with respect to spatial
inversion, for instance in bulk zinc-blend semiconductors. The interaction has
both symmetric and antisymmetric parts with respect to permutation of spin
components. The antisymmetric (Dzyaloshinskii-Moriya) interaction is the
strongest one. It contributes significantly into spin relaxation of localized
electrons; in particular, it governs low-temperature spin relaxation in n-GaAs
with the donor concentration near 10^16cm-3. The interaction must be allowed
for in designing spintronic devices, especially spin-based quantum computers,
where it may be a major source of decoherence and errors
Exact asymptotic form of the exchange interactions between shallow centers in doped semiconductors
The method developed in [L. P. Gor'kov and L. P. Pitaevskii, Sov. Phys. Dokl.
8, 788 (1964); C. Herring and M. Flicker, Phys. Rev. 134, A362 (1964)] to
calculate the asymptotic form of exchange interactions between hydrogen atoms
in the ground state is extended to excited states. The approach is then applied
to shallow centers in semiconductors. The problem of the asymptotic dependence
of the exchange interactions in semiconductors is complicated by the multiple
degeneracy of the ground state of an impurity (donor or acceptor) center in
valley or band indices, crystalline anisotropy and strong spin-orbital
interactions, especially for acceptor centers in III-V and II-VI groups
semiconductors. Properties of two coupled centers in the dilute limit can be
accessed experimentally, and the knowledge of the exact asymptotic expressions,
in addition to being of fundamental interest, must be very helpful for
numerical calculations and for interpolation of exchange forces in the case of
intermediate concentrations. Our main conclusion concerns the sign of the
magnetic interaction -- the ground state of a pair is always non-magnetic.
Behavior of the exchange interactions in applied magnetic fields is also
discussed
Quantum interference effects in p-Si1−xGex quantum wells
Quantum interference effects, such as weak localization and electronelectron interaction (EEI), have been investigated in magnetic fields up to 11 T for hole gases in a set of Si1−xGex quantum wells with 0.13 < x < 0.95. The temperature dependence of the hole phase relaxation time has been extracted from the magneto-resistance between 35 mK and 10 K. The spin-orbit effects that can be described within the Rashba model were observed in low magnetic fields. A quadratic negative magneto-resistance was observed in strong magnetic fields, due to the EEI effect. The hole-phonon scattering time was determined from hole overheating in a strong magnetic field
Magnetic-field dependence of electron spin relaxation in n-type semiconductors
We present a theoretical investigation of the magnetic field dependence of
the longitudinal () and transverse () spin relaxation times of
conduction band electrons in n-type III-V semiconductors. In particular, we
find that the interplay between the Dyakonov-Perel process and an additional
spin relaxation channel, which originates from the electron wave vector
dependence of the electron -factor, yields a maximal at a finite
magnetic field. We compare our results with existing experimental data on
n-type GaAs and make specific additional predictions for the magnetic field
dependence of electron spin lifetimes.Comment: accepted for publication in PRB, minor changes to previous manuscrip
Electron spin evolution induced by interaction with nuclei in a quantum dot
We study the decoherence of a single electron spin in an isolated quantum dot
induced by hyperfine interaction with nuclei for times smaller than the nuclear
spin relaxation time. The decay is caused by the spatial variation of the
electron envelope wave function within the dot, leading to a non-uniform
hyperfine coupling . We show that the usual treatment of the problem based
on the Markovian approximation is impossible because the correlation time for
the nuclear magnetic field seen by the electron spin is itself determined by
the flip-flop processes.
The decay of the electron spin correlation function is not exponential but
rather power (inverse logarithm) law-like. For polarized nuclei we find an
exact solution and show that the precession amplitude and the decay behavior
can be tuned by the magnetic field. The decay time is given by ,
where is the number of nuclei inside the dot. The amplitude of precession,
reached as a result of the decay, is finite. We show that there is a striking
difference between the decoherence time for a single dot and the dephasing time
for an ensemble of dots.Comment: Revtex, 11 pages, 5 figure
Bremsstrahlung radiation by a tunneling particle
We study the bremsstrahlung radiation of a tunneling charged particle in a
time-dependent picture. In particular, we treat the case of bremsstrahlung
during alpha-decay, which has been suggested as a promissing tool to
investigate the problem of tunneling times. We show deviations of the numerical
results from the semiclassical estimates. A standard assumption of a preformed
particle inside the well leads to sharp high-frequency lines in the
bremsstrahlung emission. These lines correspond to "quantum beats" of the
internal part of the wavefunction during tunneling arising from the
interference of the neighboring resonances in the well.Comment: 4 pages, 4 figure