Excitonic excitation spectra in ZnS: Cl crystal under pressure

The 3363 Å peak in the excitation spectrum of the S-A luminescence in the ZnS:Mn Cl cubic crystal at R.T. is ascribed to the A exciton. Its pressure coefficient is found as 6.4±0.2 meV/kbar, close to ρ = 6.3±0.2 meV/kbar reported for the gap in ZnS cubic crystal from the reflectivity measurements. This peak decreases by cooling and has not been observed at 85 K. The uv-excitation of the Mn-luminescence at R.T. is due to the energy transfer from the S-A to the Mn²⁺ centers, whereas the excitation peak at the exciton energy at 85 K comes from the excitation of the Mn²⁺ centers by the recombination energy of the Mn²⁺ bound excitons.     

Spin Relaxation in the quantized Hall regime in the presence of disorder

We study the spin relaxation (SR) of a two-dimensional electron gas in the quantized Hall regime and discuss the role of spatial inhomogeneity effects on the relaxation. The results are obtained for small filling factors ν?1) or when the filling factor is close to an integer. In either case, SR times are essentially determined by a smooth random potential. For small n, we predict a “magneto-confinement” resonance manifested in the enhancement of the SR rate when the Zeeman energy is close to the spacing of confinement sublevels in the low-energy wing of the disorder-broadened Landau level. In the resonant region, the B-dependence of the SR time has a peculiar nonmonotonic shape. If ν?2n+1, the SR is going nonexponentially. Under typical conditions, the calculated SR times range from 10^?8 to 10^?6 s.     

Absorption in the fractional quantum Hall regime: trion dichroism and spin polarization

We present measurements of optical interband absorption in the fractional quantum Hall regime in a GaAs quantum well in the range 0相似文献   

Cooperative order and excitation spectra in the bicomponent spin networks

A ferrimagnetic spin model composed of S = 1/2 spin-dimers and S = 5/2 spin-chains is studied by combining the bond-operator representation (for S = 1/2 spin-dimers) and Holstein-Primakoff transformation (for S = 5/2 spins). A finite interaction J _DF between the spin-dimer and the spin chain makes the spin chains ordered antiferromagnetically and the spin dimers polarized. The effective interaction between the spin chains, mediated by the spin dimers, is calculated up to the third order. The staggered magnetization in the spin dimer is shown proportional to J _DF. Due to the triplon-magnon interaction, the degeneracy of the triplons is lifted and the hybridized triplon-like excitations show different behaviors near the vanishing J _DF. A mode with longitudinal polarization is identified. The hybridized magnon-like excitations are also studied. These results are compared with the experiments on Cu₂Fe₂Ge₄O₁₃.     

Low-field phase diagram of the spin Hall effect in the mesoscopic regime

When a mesoscopic two dimensional four-terminal Hall cross bar with spin-orbit interaction (SOI) is subjected to a perpendicular uniform magnetic field B, both integer quantum Hall effect (IQHE) and mesoscopic spin Hall effect (MSHE) may exist when disorder strength W in the sample is weak. We have calculated the low field "phase diagram" of MSHE in the (B,W) plane for disordered samples in the IQHE regime. For weak disorder, MSHE conductance G(sH) and its fluctuations rms(G(sH)) vanish identically on even numbered IQHE plateaus, they have finite values on those odd numbered plateaus induced by SOI, and they have values G(sH)=1/2 and rms(G(sH))=0 on those odd numbered plateaus induced by Zeeman energy. At larger disorders, the system crosses over into a regime where both G(sH) and rms(G(sH)) are finite, a chaotic regime, and finally a localized regime.     

Probing spin physics in the quantum Hall regime by heat capacity and magnetotransport measurements

We review recent heat capacity and magnetotransport experiments on GaAs/AlGaAs heterostructures containing multilayer two-dimensional electron systems (2DESs) in the quantum Hall regime. Emphasis in this article is on the study of the heat capacity near Landau level filling factor ν=1. We also present a detailed survey of the development of the quantum Hall effect in tilted-magnetic fields for ν≲2. Among the novel phenomena we address is the strong coupling between the nuclear spins and the electrons associated with the spin phase transitions of the 2DES at ν=4/3 and near ν=1. To cite this article: S. Melinte et al., C. R. Physique 3 (2002) 667–676.     

Light scattering observations of spin reversal excitations in the fractional quantum Hall regime

Resonant inelastic light scattering experiments access the low lying excitations of electron liquids in the fractional quantum Hall regime in the range 2/5≥ν≥1/3. Modes associated with changes in the charge and spin degrees of freedom are measured. Spectra of spin reversed excitations at filling factor ν?1/3 and at ν?2/5 identify a structure of lowest spin-split Landau levels of composite fermions (CFs) that is similar to that of electrons. Observations of spin wave excitations enable determinations of energies required to reverse spin. The spin reversal energies obtained from the spectra illustrate the significant residual interactions of composite fermions. At ν=1/3 energies of spin reversal modes are larger but relatively close to spin conserving excitations that are linked to activated transport. Predictions of composite fermion theory are in good quantitative agreement with experimental results.     

Helical nuclear spin order in a strip of stripes in the quantum Hall regime

We investigate nuclear spin effects in a two-dimensional electron gas in the quantum Hall regime modeled by a weakly coupled array of interacting quantum wires. We show that the presence of hyperfine interaction between electron and nuclear spins in such wires can induce a phase transition, ordering electrons and nuclear spins into a helix in each wire. Electron-electron interaction effects, pronounced within the one-dimensional stripes, boost the transition temperature up to tens to hundreds of millikelvins in GaAs. We predict specific experimental signatures of the existence of nuclear spin order, for instance for the resistivity of the system at transitions between different quantum Hall plateaus.     

Fermionization of grassmannians and the quantized Hall effect

The rules of fermionization of grassmannian sigma models with instanton terms are derived. Their application to the quantized Hall effect is discussed.     

Intrinsic spin Hall effect in silicene: transition from spin Hall to normal insulator

An intrinsic contribution to the spin Hall effect in two‐dimensional silicene is considered theoretically within the linear response theory and Green's function formalism. When an external voltage normal to the silicene plane is applied, the spin Hall conductivity is shown to reveal a transition from the spin Hall insulator phase at low bias to the conventional insulator phase at higher voltages. This transition resembles the recently reported phase transition in bilayer graphene. The spin–orbit interaction responsible for this transition in silicene is much stronger than in graphene, which should make the transition observable experimentally. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Contribution to the theory of spin relaxation at finite temperatures in the odd-filling quantum Hall effect regime

Spin relaxation in a two-dimensional electron gas (2D EG) is treated as the establishment of equilibrium in a gas of spin excitons as a result of processes that change the number of spin excitons. Coalescence is the dominant channel above a temperature of the order of 1 K. The coalescence of excitons can occurr as a result of spin-orbit and Coulomb interactions in the 2D EG. The rate of coalescence falls exponentially at low temperatures. The relaxation time is calculated, and the critical temperature below which the main annihilation process becomes that due to the exciton-phonon interaction is determined. Pis’ma Zh. éksp. Teor. Fiz. 70, No. 8, 531–536 (25 October 1999)     

Current-induced spin polarization and the spin Hall effect: A quasiclassical approach

The quasiclassical Green function formalism is used to describe charge and spin dynamics in the presence of spin-orbit coupling. We review the results obtained for the spin Hall effect on restricted geometries. The role of boundaries is discussed in the framework of spin diffusion equations.     

Disorder and the theory of the fractionally quantized Hall effect

In a recent article we showed that weak disorder does not change the ground states of a system of interacting electrons on a torus in a strong magnetic field at a filling factorf ₀, if the denominator off ₀ is odd and small. At filling factors near but not equalf ₀ disorder becomes important. We show that the ground states and the low excited states of such a system may be constructed from the ground states atf ₀ through adding localized electrons or holes. These states have the same degeneracy as the ground states atf ₀ and lead to the same value of the Hall conductance.