3,580 research outputs found
Coherent spin dynamics of electrons and excitons in nanostructures
The studies of spin phenomena in semiconductor low dimensional systems have
grown into the rapidly developing area of the condensed matter physics:
spintronics. The most urgent problems in this area, both fundamental and
applied, are the creation of charge carrier spin polarization and its detection
as well as electron spin control by nonmagnetic methods. Here we present a
review of recent achievements in the studies of spin dynamics of electrons,
holes and their complexes in the pump-probe method. The microscopic mechanisms
of spin orientation of charge carriers and their complexes by short circularly
polarized optical pulses and the formation processes of the spin signals of
Faraday and Kerr rotation of the probe pulse polarization plane as well as
induced ellipticity are discussed. A special attention is paid to the
comparison of theoretical concepts with experimental data obtained on the
n-type quantum well and quantum dot array samples.Comment: Review, 25 pages, 18 figures; Physics of the Solid State 54, 1 (2012
Spin fluctuations of non-equilibrium electrons and excitons in semiconductors
Effects related with deviations from thermodynamic equilibrium take a special
place in the modern physics. Among those, non-equilibrium phenomena in quantum
systems attract the highest interest. To date, the experimental technique of
spin noise spectroscopy has became quite widespread, which makes possible to
observe spin fluctuations of charge carriers in semiconductors both in
equilibrium and non-equilibrium conditions. It calls for development of the
theory of spin fluctuations of electrons and electron-hole complexes for
non-equilibrium conditions. In this paper we consider a range of physical
situations where a deviation from an equilibrium becomes pronounced in the spin
noise. A general method of calculation of electron and exciton spin
fluctuations in non-equilibrium state is proposed. A short review of
theoretical and experimental results in this area is given.Comment: Special JETP issue dedicated to the 85th birthday of Prof. L. V.
Keldysh; 12 pages, 7 figure
Fine structure of two-electron states in single and double quantum dots
Energy spectrum fine structure of triplet two-electron states is investigated
theoretically. Spin-orbit interaction induced terms in the effective
Hamiltonian of electron-electron interaction are derived for zinc-blende
lattice semiconductor nanostructures: quantum wells and quantum dots. The
effects of bulk and structural inversion asymmetry are taken into account.
Simple analytical expressions describing the splittings of the two-electron
states localized in a single quantum dot and in a lateral double quantum dot
are derived. The spin degeneracy of triplet states is shown to be completely
lifted by the spin-orbit interaction. An interplay of the conduction band spin
splitting and the spin-orbit terms in electron-electron interaction is
discussed. The photoluminescence spectra of hot trions and of doubly charged
excitons are calculated and are shown to reveal the fine structure of
two-electron states.Comment: 9 pages, 6 figure
Spin noise of localized electrons: Interplay of hopping and hyperfine interaction
The theory of spin fluctuations is developed for an ensemble of localized
electrons taking into account both hyperfine interaction of electron and
nuclear spins and electron hopping between the sites. The analytical expression
for the spin noise spectrum is derived for arbitrary relation between the
electron spin precession frequency in the field of the nuclear fluctuation and
the hopping rate. An increase in the hopping rate results in the drastic change
of the spin noise spectrum. The effect of an external magnetic field is briefly
addressed.Comment: 5 pages, 3 figure
Phonon wind and drag of excitons in monolayer semiconductors
We study theoretically the non-equilibrium exciton transport in monolayer
transition metal dichalcogenides. We consider the situation where excitons
interact with non-equilibrium phonons, e.g., under the conditions of localized
excitation where a ``hot spot'' in formed. We develop the theory of the exciton
drag by the phonons and analyze in detail the regimes of diffusive propagation
of phonons and ballistic propagation of phonons where the phonon wind is
formed. We demonstrate that a halo-like spatial distribution of excitons akin
observed in [Phys. Rev. Lett. 120, 207401 (2018)] can be formed as a result of
the exciton drag by non-equilibrium phonons or Seebeck effect.Comment: 13 pages, 5 figure
Spin-dependent coherent transport of two-dimensional excitons
We propose a theory of interference contributions to the two-dimensional
exciton diffusion coefficient. The theory takes into account four spin states
of the heavy-hole exciton. An interplay of the single particle, electron and
hole, spin splittings with the electron-hole exchange interaction gives rise to
either localization or antilocalization behavior of excitons depending on the
system parameters. Possible experimental manifestations of exciton interference
are discussed.Comment: 7 pages, 2 figure
Linear optics, Raman scattering, and spin noise spectroscopy
Spin noise spectroscopy (SNS) is a new method for studying magnetic resonance
and spin dynamics based on measuring the Faraday rotation noise. In strong
contrast with methods of nonlinear optics, the spectroscopy of spin noise is
considered to be essentially nonperturbative. Presently, however, it became
clear that the SNS, as an optical technique, demonstrates properties lying far
beyond the bounds of conventional linear optics. Specifically, the SNS shows
dependence of the signal on the light power density, makes it possible to
penetrate inside an inhomogeneously broadened absorption band and to determine
its homogeneous width, allows one to realize an effective pump-probe
spectroscopy without any optical nonlinearity, etc. This may seem especially
puzzling when taken into account that SNS can be considered just as a version
of Raman spectroscopy, which is known to be deprived of such abilities. In this
paper, we clarify this apparent inconsistency.Comment: 7+ pages, 3 figure
Topological spin phases of trapped Rydberg excitons in CuO
We study theoretically Rydberg excitons in one-dimensional chains of traps in
CuO coupled via the van der Waals interaction. The triplet of optically
active -shell states acts as an effective spin- and the interactions
between the excitons are strongly spin-dependent. We predict that the system
{has the} topological Haldane phase with the diluted antiferromagnetic order,
long-range string correlations, and finite excitation gap. We also analyze the
effect of the trap geometry and interactions anisotropy on the Rydberg exciton
spin states and demonstrate that a rich spin phase diagram can be realized
showing high tunability of the Rydberg exciton platform.Comment: main text (5 pages, 4 figures) + supplement (5 pages, 5 figures
Cavity polaritons: Classical behaviour of a quantum parametric oscillator
We address theoretically the optical parametric oscillator based on
semiconductor cavity exciton-polaritons under a pulsed excitation. A
"hyperspin" formalism is developed which allows, in the case of large number of
polaritons, to reduce quantum dynamics of the parametric oscillator
wavefunction to the Liouville equation for the classical probability
distribution. Implications for the statistics of polariton ensembles are
analyzed.Comment: 8 pages, 5 figure
Quantum and classical multiple scattering effects in spin dynamics of cavity polaritons
The transport properties of exciton-polaritons are studied with allowance for
their polarization. Both classical multiple scattering effects and quantum
effects such as weak localization are taken into account in the framework of a
generalized kinetic equation. The longitudinal-transverse (TE-TM) splitting of
polariton states which plays role analogous to the spin-orbit splitting in
electron systems is taken into account. The developed formalism is applied to
calculate the particle and spin diffusion coefficients of exciton-polaritons,
spin relaxation rates and the polarization conversion efficiency under the
conditions of the optical spin Hall effect. In contrast to the electron
systems, strong spin splitting does not lead to the antilocalization behavior
of the particle diffusion coefficient, while quantum corrections to spin
diffusion and polarization conversion can be both negative and positive
depending on the spin splitting value.Comment: 10 pages, 5 figure
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