Electron transport and optical properties of shallow GaAs/InGaAs/GaAs quantum wells with a thin central AlAs barrier

Shallow GaAs/InGaAs/GaAs quantum well structures with and without a three monolayer thick AlAs central barrier have been investigated for different well widths and Si doping levels. The transport parameters are determined by resistivity measurements in the temperature range 4-300 K and magnetotransport in magnetic fields up to 12 T. The (subband) carrier concentrations and mobilities are extracted from the Hall data and Shubnikov-de Haas oscillations. We find that the transport parameters are strongly affected by the insertion of the AlAs central barrier. Photoluminescence spectra, measured at 77 K, show an increase of the transition energies upon insertion of the barrier. The transport and optical data are analyzed with help of self-consistent calculations of the subband structure and envelope wave functions. Insertion of the AlAs central barrier changes the spatial distribution of the electron wave functions and leads to the formation of hybrid states, i.e. states which extend over the InGaAs and the delta-doped layer quantum wells.Comment: 14 pages, pdf fil

Quantum critical behaviour of the plateau-insulator transition in the quantum Hall regime

High-field magnetotransport experiments provide an excellent tool to investigate the plateau-insulator phase transition in the integral quantum Hall effect. Here we review recent low-temperature high-field magnetotransport studies carried out on several InGaAs/InP heterostructures and an InGaAs/GaAs quantum well. We find that the longitudinal resistivity $\rho_{xx}$ near the critical filling factor $\nu_{c}$ ~ 0.5 follows the universal scaling law $\rho_{xx}(\nu, T) \propto exp[-\Delta \nu/(T/T_{0})^{\kappa}]$, where $\Delta \nu =\nu -\nu_{c}$. The critical exponent $\kappa$ equals $0.56 \pm 0.02$, which indicates that the plateau-insulator transition falls in a non-Fermi liquid universality class.Comment: 8 pages, accepted for publication in Proceedings of the Yamada Conference LX on Research in High Magnetic Fields (August 16-19, 2006, Sendai

Tilted magnetic field quantum magnetotransport in the double quantum well with a sizable bulk g-factor: InxGa1-xAs/GaAs

Rich patterns of transformations in the structure of quantum Hall (QH) effect and magnetoresistivity under tilted magnetic fields were obtained in the InxGa1-xAs/GaAs double quantum well at mK temperatures. Local features correspond to the calculated intersections of Landau levels from different subbands and are due to the sharp motion of their crossing points with parallel field component. An incipient quenching with parallel field of the filling factor v = 3 QH state is revealed, which should be due to suppression of the interlayer connection. The observed peculiar monotonous shift in perpendicular fields with increasing in-plain field of the peak between QH states v = 1 and 2 as well as an unusual minimum on some QH plateaus are probably beyond the single particle treatment

Evolution of the spin-split quantum Hall states with magnetic field tilt in the InAs-based double quantum wells

Development of quantum Hall peculiarities due to mobility gap between spin-split magnetic levels with addition of the parallel magnetic field component B|| is analyzed in double quantum wells (DQW) created in InGaAs/GaAs and InAs/AlSb heterosystems chosen due to their relatively large bulk g-factors. In InGaAs/GaAs DQWs, the nonmonotonous behavior of these peculiarities is observed and explained within single-electron approach in terms of competition between enhanced spin splitting and localization of electrons in the layers of DQW with increased B||. In InAs/AlSb DQW, the tunneling connection between the layers is very weak due to high barrier, nevertheless the collective odd-numbered peculiarities are revealed that exist due to spontaneous interlayer phase coherence. B|| destroys these states that is manifested, in particular, in the suppression of the peculiarity for filling factor v = 3

HERV-K Modulates the Immune Response in ALS Patients

Human endogenous retrovirus (HERV)-K env-su glycoprotein has been documented in amyotrophic lateral sclerosis (ALS), where HERV-K env-su 19–37 antibody levels significantly correlated with clinical measures of disease severity. Herein, we investigated further the humoral and cell-mediated immune response against specific antigenic peptides derived from HERV-K in ALS. HERV-K env glycoprotein expression on peripheral blood mononuclear cells (PBMCs) membrane and cytokines and chemokines after stimulation with HERV-K env 19–37 and HERV-K env 109–126 were quantified in patients and healthy controls (HCs). HERV-K env glycoprotein was more expressed in B cells and NK cells of ALS patients compared to HCs, whereas HERV-K env transcripts were similar in ALS and HCs. In ALS patients, specific stimulation with HERV-K env 109–126 peptide showed a higher expression of IL-6 by CD19/B cells. Both peptides, however, were able to induce a great production of IFN-γ by stimulation CD19/B cells, and yielded a higher expression of MIP-1α and a lower expression of MCP-1. HERV-K env 19–37 peptide induced a great production of TNF-α in CD8/T cells. In conclusion, we observed the ability of HERV-K to modulate the immune system, generating mediators mainly involved in proinflammatory response