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Register a new userMagnetotunneling Between Two-dimensional Electron Gases in InAs-AlSb-GaSb Heterostructures
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We have observed that the tunneling magnetoconductance between two-dimensional (2D) electron gases formed at nominally identical InAs-AlSb interfaces most often exhibits two sets of Shubnikov-de Haas oscillations with almost the same frequency. This result is explained quantitatively with a model of the conductance in which the 2D gases have different densities and can tunnel between Landau levels with different quantum indices. When the epitaxial growth conditions of the interfaces are optimized, the zero-bias magnetoconductance shows a single set of oscillations, thus proving that the asymmetry between the two electron gases can be eliminated.
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We have measured the zero-bias differential tunneling conductance of InAs/AlSb/GaS b/AlSb/InAs heterostructures at low temperatures (1.7K < T < 60K) and unde r a magnetic field at various angles with the heterostructures interfaces. Shubni kov-de Haas oscillations in the magnetoconductance reveal the two-dimensional (2D) character of the electrons accumulated at the InAs interfaces and yield their num ber in each of them. The temperature dependence of the oscillations suggests the f ormation of a field-induced energy gap at the Fermi level, similar to that observe d before in simpler 2D-2D tunneling systems. A calculation of the magnetoconductan ce that considers different 2D densities in the two InAs electrodes agrees with th e main observations, but fails to explain features that might be related to the pr esence of 2D holes in the GaSb region.
We examine the possibility of intrinsic interface states bound to the plane of In-Sb chemical bonds at InAs/AlSb interfaces. Careful parameterization of the bulk materials in the frame of the extended basis spds^* tight-binding model and recent progress in predictions of band offsets severely limit the span of tight-binding parameters describing this system. We find that a heavy-hole like interface state bound to the plane of In-Sb bonds exists for a large range of values of the InSb/InAs band offset.
A new approach to the growth of diluted magnetic semiconductors with two dimensional electron gas in InAs quantum well has been developed. The method is based on molecular-beam epitaxy of coherent hybrid AlSb/InAs/(Zn,Mn)Te heterostructures with a III-V/II-VI interface inside. The giant Zeeman splitting of the InAs conduction band caused by exchange interaction with Mn2+ ions has been proved by measuring the microwave radiation induced spin polarized electric currents.
We study quantum point contacts in two-dimensional topological insulators by means of quantum transport simulations for InAs/GaSb heterostructures and HgTe/(Hg,Cd)Te quantum wells. In InAs/GaSb, the density of edge states shows an oscillatory decay as a function of the distance to the edge. This is in contrast to the behavior of the edge states in HgTe quantum wells, which decay into the bulk in a simple exponential manner. The difference between the two materials is brought about by spatial separation of electrons and holes in InAs/GaSb, which affects the magnitudes of the parameters describing the particle-hole asymmetry and the strength of intersubband coupling within the Bernevig-Hughes-Zhang model. We show that the character of the wave function decay impacts directly the dependence of the point contact conductance on the constriction width and the Fermi energy, which can be verified experimentally and serve to determine accurately the values of relevant parameters. In the case of InAs/GaSb heterostructures the conductance magnitude oscillates as a function of the constriction width following the oscillations of the edge state penetration, whereas in HgTe/(Hg,Cd)Te quantum wells a single switching from transmitting to reflecting contact is predicted.
We have studied a series of InAs/GaSb coupled quantum wells using magneto-infrared spectroscopy for high magnetic fields up to 33T within temperatures ranging from 4K to 45K in both Faraday and tilted field geometries. This type of coupled quantum wells consists of an electron layer in the InAs quantum well and a hole layer in the GaSb quantum well, forming the so-called two dimensional electron-hole bilayer system. Unlike the samples studied in the past, the hybridization of the electron and hole subbands in our samples is largely reduced by having narrower wells and an AlSb barrier layer interposed between the InAs and the GaSb quantum wells, rendering them weakly hybridized. Previous studies have revealed multiple absorption modes near the electron cyclotron resonance of the InAs layer in moderately and strongly hybridized samples, while only a single absorption mode was observed in the weakly hybridized samples. We have observed a pair of absorption modes occurring only at magnetic fields higher than 14T, which exhibited several interesting phenomena. Among which we found two unique types of behavior that distinguishes this work from the ones reported in the literature. This pair of modes is very robust against rising thermal excitations and increasing magnetic fields alligned parallel to the heterostructures. While the previous results were aptly explained by the antilevel crossing gap due to the hybridization of the electron and hole wavefunctions, i.e. conduction-valence Landau level mixing, the unique features reported in this paper cannot be explained within the same concept. The unusual properties found in this study and their connection to the known models for InAs/GaSb heterostructures will be disccused; in addition, several alternative ideas will be proposed in this paper and it appears that a spontaneous phase separation can account for most of the observed features.
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