Metal-Insulator oscillations in a Two-dimensional Electron-Hole system

The electrical transport properties of a bipolar InAs/GaSb system have been studied in magnetic field. The resistivity oscillates between insulating and metallic behaviour while the quantum Hall effect shows a digital character oscillating from 0 to 1 conducatance quantum e^2/h. The insulating behaviour is attributed to the formation of a total energy gap in the system. A novel looped edge state picture is proposed associated with the appearance of a voltage between Hall probes which is symmetric on magnetic field reversal.Comment: 4 pages, 5 Postscript figures: revised versio

Tunneling transverse to a magnetic field, and how it occurs in correlated 2D electron systems

We investigate tunneling decay in a magnetic field. Because of broken time-reversal symmetry, the standard WKB technique does not apply. The decay rate and the outcoming wave packet are found from the analysis of the set of the particle Hamiltonian trajectories and its singularities in complex space. The results are applied to tunneling from a strongly correlated 2D electron system in a magnetic field parallel to the layer. We show in a simple model that electron correlations exponentially strongly affect the tunneling rate.Comment: 4 pages, 3 figure

Tunneling decay in a magnetic field

We provide a semiclassical theory of tunneling decay in a magnetic field and a three-dimensional potential of a general form. Because of broken time-reversal symmetry, the standard WKB technique has to be modified. The decay rate is found from the analysis of the set of the particle Hamiltonian trajectories in complex phase space and time. In a magnetic field, the tunneling particle comes out from the barrier with a finite velocity and behind the boundary of the classically allowed region. The exit location is obtained by matching the decaying and outgoing WKB waves at a caustic in complex configuration space. Different branches of the WKB wave function match on the switching surface in real space, where the slope of the wave function sharply changes. The theory is not limited to tunneling from potential wells which are parabolic near the minimum. For parabolic wells, we provide a bounce-type formulation in a magnetic field. The theory is applied to specific models which are relevant to tunneling from correlated two-dimensional electron systems in a magnetic field parallel to the electron layer.Comment: 16 pages, 11 figure

Giant negative magnetoresistance in semiconductors doped by multiply charged deep impurities

A giant negative magnetoresistance has been observed in bulk germanium doped with multiply charged deep impurities. Applying a magnetic field the resistance may decrease exponentially at any orientation of the field. A drop of the resistance as much as about 10000% has been measured at 6 T. The effect is attributed to the spin splitting of impurity ground state with a very large g-factor in the order of several tens depending on impurity.Comment: 4 pages, 4 figure

Shubnikov-De Haas study in laterally constricted GaAs-AlGaAs heterojunctions$

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Interface composition dependence of the band offset in InAs/GaSb

We have performed 4 K magnetotransport measurements on intrinsic InAs/GaSb multi quantum wells (MQWs) under hydrostatic pressure. Through careful configuration of the growth we are able to produce samples that have differing interface monolayers (either InSb or GaAs). Analysing the data to calculate the band overlap (Delta), we find that InSb-like samples have an overlap 30 meV larger than GaAs-like in good agreement with recent theoretical predictions

Optical probing of the minigap in InAs/GaSb superlattices

We report large modulations in the far infrared absorption of semimetallic InAs/GaSb superlattices in parallel field. The strong absorption is attributed to direct transitions across the minigap at the point where the electron and hole dispersions anticross. The measured minigap energy is found to be in the range 3-10 meV depending on the structure of the sample. The optical results are compared to parallel field magnetoresistance measurements and also to theory using an 8 band k . p calculation. (C) 1998 Elsevier Science B.V. All rights reserved