Longitudinal conductivity and transverse charge redistribution in coupled quantum wells subject to in-plane magnetic fields

In double quantum wells electrons experience a Lorentz force oriented perpendicular to the structure plane when an electric current is driven perpendicular to the direction of an in-plane magnetic field. Consequently, the excess charge is accumulated in one of the wells. The polarization of a bilayer electron system and the corresponding Hall voltage are shown to contribute substantially to the in-plane conductivity.Comment: 3 pages, 2 figure

Novel critical field in magneto-resistance oscillation of 2DEG in asymmetric GaAs/AlGaAs double wells measured as a function of the in-plane magnetic field

We have investigated the magnetoresistance of strongly asymmetric double-well structures formed by a thin AlGaAs barrier grown far from the interface in the GaAs buffer of standard heterostructures. In magnetic fields oriented parallel to the electron layers, the magnetoresistance exhibits an oscillation associated with the depopulation of the higher occupied subband and with the field-induced transition into a decoupled bilayer. In addition, the increasing field transfers electrons from the triangular to rectangular well and, at high enough field value, the triangular well is emptied. Consequently, the electronic system becomes a single layer which leads to a sharp step in the density of electron states and to an additional minimum in the magnetoresistance curve.Comment: 3 pages, 3 figure

Permittivity model selection based on size and quantum-size effects in gold films

The article explores optical properties of nanostructures containing spherical gold nanoparticles of various radii. We explore the particle radius as a criterion to select a permittivity model aimed at describing optical absorption spectra of gold granules. The experiments showed splitting of the absorption band of granular gold films to form a second absorption peak. The first peak is associated with the phenomenon of plasmon resonance, while the second one reflects quantum hybridization of energy levels in gold. Quantum effects were shown to prevail over size effects at a granule diameter of about 5-6 nm. The Mie theory gives a rigorous solution for the scattered electromagnetic field on a sphere taking into account optical properties of the latter, however, it does not specify criteria of selecting a model to calculate dielectric permittivity. Both calculations and experiments confirmed the limiting diameter of gold nanoparticles where the Hampe-Shklyarevsky model is applied. Meanwhile, this model was still unable to predict splitting of the plasma absorption band. The data presented in the article can be used for a predetermined local field enhancement in composite media consisting of a biolayer and metal nanoparticles.Comment: 11 pages, 4 figure

Quasi two-dimensional carriers in dilute-magnetic-semiconductor quantum wells under in-plane magnetic field

Due to the competition between spatial and magnetic confinement, the density of states of a quasi two-dimensional system deviates from the ideal step-like form both quantitatively and qualitatively. We study how this affects the spin-subband populations and the spin-polarization as functions of the temperature, $T$, and the in-plane magnetic field, $B$, for narrow to wide dilute-magnetic-semiconductor quantum wells. We focus on the quantum well width, the magnitude of the spin-spin exchange interaction, and the sheet carrier concentration dependence. We look for ranges where the system is completely spin-polarized. Increasing $T$, the carrier spin-splitting, $U_{o\sigma}$, decreases, while increasing $B$, $U_{o\sigma}$ increases. Moreover, due to the density of states modification, all energetically higher subbands become gradually depopulated.Comment: 3 pages, 3 figure

In-plane Magnetic Field Dependent Magnetoresistance of Gated Asymmetric Double Quantum Wells

We have investigated experimentally the magnetoresistance of strongly asymmetric double-wells. The structures were prepared by inserting a thin Al$_{0.3}$Ga$_{0.7}$As barrier into the GaAs buffer layer of a standard modulation-doped GaAs/Al$_{0.3}$Ga$_{0.7}$As heterostructure. The resulting double-well system consists of a nearly rectangular well and of a triangular well coupled by tunneling through the thin barrier. With a proper choice of the barrier parameters one can control the occupancy of the two wells and of the two lowest (bonding and antibonding) subbands. The electron properties can be further influenced by applying front- or back-gate voltage.Comment: 4 pages, 5 figures, elsart/PHYEAUTH macros; to be presented on the EP2DS-15 Conference in Nara, Japan. Revised version. To appear in Physica

Magnetoresistance and electronic structure of asymmetric GaAs/AlGaAs double quantum wells in the in-plane/tilted magnetic field

Bilayer two-dimensional electron systems formed by a thin barrier in the GaAs buffer of a standard heterostructure were investigated by magnetotransport measurements. In magnetic fields oriented parallel to the electron layers, the magnetoresistance exhibits an oscillation associated with the depopulation of the higher occupied subband and the field-induced transition into a decoupled bilayer. Shubnikov-de Haas oscillations in slightly tilted magnetic fields allow to reconstruct the evolution of the electron concentration in the individual subbands as a function of the in-plane magnetic field. The characteristics of the system derived experimentally are in quantitative agreement with numerical self-consistent-field calculations of the electronic structure.Comment: 6 pages, 5 figure