271 research outputs found
Optical Spin Orientation in Strained Superlattices
Optical orientation in the strained semiconductor superlattices is
investigated theoretically. The dependence of the features in spin-polarization
spectra on the structure parameters is clarified. The value of polarization in
the first polarization maximum in the SL structures is shown to grow with the
splitting between the hh- and lh- states of the valence band, the joint strain
and confinement effects on the hh1- lh1 splitting being strongly influenced by
the tunneling in the barriers. In strained structures with high barriers for
the holes initial polarization can exceed 95 %. Calculated polarization spectra
are close to the experimental spectra of polarized electron emission.Comment: 20 pages, 8 figure
Weak localization of holes in high-mobility heterostructures
Theory of weak localization is developed for two-dimensional holes in
semiconductor heterostructures. Ballistic regime of weak localization where the
backscattering occurs from few impurities is studied with account for
anisotropic momentum scattering of holes. The transition from weak localization
to anti-localization is demonstrated for long dephasing times. For stronger
dephasing the conductivity correction is negative at all hole densities due to
non-monotonous dependence of the spin relaxation time on the hole wavevector.
The anomalous temperature dependent correction to the conductivity is
calculated. We show that the temperature dependence of the conductivity is
non-monotonous at moderate hole densities.Comment: 5 pages, 4 figure
Theorem about the number and structure of the singular points n-dimensional dynamical system of population dynamics Lotka-Volterra in context of informational analysis and modeling
By elementary methods of combinatorial mathematics and uniqueness of solutions systems of linear algebraic equations for non degenerate cases proved a theorem about the number and structure of the singular points of n-dimensional dynamical system of population a dynamics Lotka-Volterra model. Showed that the number of singular points for this system is equal to 2 and their structure on a combination of zero nand nonzero coordinates coincides with the binomial coefficientsyesBelgorod State Universit
Characterization of deep impurities in semiconductors by terahertz tunneling ionization
Tunneling ionization in high frequency fields as well as in static fields is suggested as a method for the characterization of deep impurities in semiconductors. It is shown that an analysis of the field and temperature dependences of the ionization probability allows to obtain defect parameters like the charge of the impurity, tunneling times, the Huang–Rhys parameter, the difference between optical and thermal binding energy, and the basic structure of the defect adiabatic potentials. Compared to static fields, high frequency electric fields in the terahertz-range offer various advantages, as they can be applied contactlessly and homogeneously even to bulk samples using the intense radiation of a high power pulsed far-infrared laser. Furthermore, impurity ionization with terahertz radiation can be detected as photoconductive signal with a very high sensitivity in a wide range of electric field strengths
Optical control of spin coherence in singly charged (In,Ga)As/GaAs quantum dots
Electron spin coherence has been generated optically in n-type modulation
doped (In,Ga)As/GaAs quantum dots (QDs) which contain on average a single
electron per dot. The coherence arises from resonant excitation of the QDs by
circularly-polarized laser pulses, creating a coherent superposition of an
electron and a trion state. Time dependent Faraday rotation is used to probe
the spin precession of the optically oriented electrons about a transverse
magnetic field. Spin coherence generation can be controlled by pulse intensity,
being most efficient for (2n+1)pi-pulses.Comment: 5 pages, 4 figure
Tetrapotassium diantimony(III) tin(IV) tetradecafluoride
The title compound, K4Sb2SnF14, is built from anionic layers, with an overall composition of [Sb2SnF14]4− extending parallel to the ac plane, and K+ cations. The layers are made up from vertex-sharing centrosymmetric SnF6 octahedra and Sb2F12 dimers. The Sn—F distances are in the range 1.9581 (14)–1.9611 (17) Å. The Sb polyhedra contain three short terminal Sb—F bonds [1.9380 (14)–2.0696 (15) Å], one short bridging bond [2.0609 (17) Å], one bridging bond of medium length [2.7516 (15) Å], and two longer bridging bonds [3.0471 (18) and 3.117 (2) Å]. The K+ ions are coordinated by F atoms with coordination numbers 10 and 8, and K—F bond lengths are in the range 2.6235 (16)–3.122 (2) Å
Spin-orbit terms in multi-subband electron systems: A bridge between bulk and two-dimensional Hamiltonians
We analyze the spin-orbit terms in multi-subband quasi-two-dimensional
electron systems, and how they descend from the bulk Hamiltonian of the
conduction band. Measurements of spin-orbit terms in one subband alone are
shown to give incomplete information on the spin-orbit Hamiltonian of the
system. They should be complemented by measurements of inter-subband spin-orbit
matrix elements. Tuning electron energy levels with a quantizing magnetic field
is proposed as an experimental approach to this problem.Comment: Typos noticed in the published version have been corrected and
several references added. Published in the special issue of Semiconductors in
memory of V.I. Pere
The Nuclear Spin Nanomagnet
Linearly polarized light tuned slightly below the optical transition of the
negatively charged exciton (trion) in a single quantum dot causes the
spontaneous nuclear spin polarization (self-polarization) at a level close to
100%. The effective magnetic field of spin-polarized nuclei brings the optical
transition energy into resonance with photon energy. The resonantly enhanced
Overhauser effect sustains the stability of the nuclear self-polarization even
in the absence of spin polarization of the quantum dot electron. As a result
the optically selected single quantum dot represents a tiny magnet with the
ferromagnetic ordering of nuclear spins - the nuclear spin nanomagnet.Comment: 19 pages, including 3 figures. Short version has been accepted for
publication in Physical Review Letter
Stabilizing effect of nuclear quadrupole interaction on the polarization of electron-nuclear spin system in a quantum dot
Nuclear quadrupole interaction extends the limits imposed by hyperfine
interaction on the spin coherence of the electron and nuclei in a quantum dot.
The strain-induced nuclear quadrupole interaction suppresses the nuclear spin
flip and makes possible the zero-field dynamic nuclear polarization in
self-organized InP/InGaP quantum dots. The direction of the effective nuclear
magnetic field is fixed in space, thus quenching the magnetic depolarization of
the electron spin in the quantum dot. The quadrupole interaction suppresses the
zero-field electron spin decoherence also for the case of non-polarized nuclei.
These results provide a new vision of the role of the nuclear quadrupole
interaction in nanostructures: it elongates the spin memory of the
electron-nuclear system.Comment: 18 pages including 3 figures. Shortened version has been accepted for
publication in Physical Review Letter
Intrinsic electric polarization in spin-orbit coupled semiconductor heterostructures
We present Maxwell equations with source terms for the electromagnetic field
interacting with a moving electron in a spin-orbit coupled semiconductor
heterostructure. We start with the eight--band model and
derive the electric and magnetic polarization vectors using the Gordon--like
decomposition method. Next, we present the effective
Lagrangian for the nonparabolic conduction band electrons interacting with
electromagnetic field in semiconductor heterostructures with abrupt interfaces.
This Lagrangian gives rise to the Maxwell equations with source terms and
boundary conditions at heterointerfaces as well as equations for the electron
envelope wave function in the external electromagnetic field together with
appropriate boundary conditions. As an example, we consider spin--orbit effects
caused by the structure inversion asymmetry for the conduction electron states.
We compute the intrinsic contribution to the electric polarization of the
steady state electron gas in asymmetric quantum well in equilibrium and in the
spin Hall regime. We argue that this contribution, as well as the intrinsic
spin Hall current, are not cancelled by the elastic scattering processes.Comment: 12 pages, 3 figure
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