The electronic structure of InAs/AlSb/GaSb quantum wells embedded in AlSb barriers and in the presence of a perpendicular magnetic field is studied theoretically within the 14-band ?? · ?? approach without making the axial approximation.At zero magnetic field, for a quantum well with a wide In As layer and a wide GaSb layer, the energy of an electron-like subband can be lower than the energy of hole-like subbands. As the strength of the magnetic field increases, the Landau levels of this electron-like subband grow in energy and intersect the Landau levels of the hole-like subbands. The electron–hole hybridization leads to a series of anti-crossing splittings of the Landau levels. The magnetic field dependence of some dominant transitions is shown with their corresponding initial-states and final-states indicated. The dominant transitions at high fields can be roughly viewed as two spin-split Landau level transitions with many electron–hole hybridization-induced splittings. When the magnetic field is tilted, the electron-like Landau level transitions show additional anti-crossing splittings due to the subband-Landau level coupling.
The exchange effect and the magneto-plasmon mode dispersion are studied theoretically for an anisotropic twodimensional electronic system in the presence of a uniform perpendicular magnetic field.Employing an effective lowenergy model with anisotropic effective masses,which is relevant for a monolayer of phosphorus,the exchange effect due to the electron-electron interaction is treated within the self-consistent Hartree-Fock approximation.The magnetoplasmon mode dispersion is obtained by solving a Bethe-Salpeter equation for the electron density-density correlation function within the ladder diagram approximation.It is found that the exchange effect is reduced in the anisotropic system in comparison with the isotropic one.The magneto-plasmon mode dispersion shows a clear dependence on the direction of the wave vector.
We investigate the efficiency of electrical manipulation in a two-dimensional topological insulator by inspecting the electronic states of a lateral electrical potential superlattice in the system. The spatial distribution of the electron density in the system can be tuned by changing the strength of the externally applied lateral electrical superlattice potential. This provides us the information about how efficiently one can manipulate the electron motion inside a two-dimensional topological insulator. Such information is important in designing electronic devices, e.g., an electric field effect transistor made of the topological insulator. The electronic states under various conditions are examined carefully. It is found that the dispersion of the mini-band and the electron distribution in the potential well region both display an oscillatory behavior as the potential strength of the lateral superlattice increases. The probability of finding an electron in the potential well region can be larger or smaller than the average as the potential strength varies. These features can be attributed to the coupled multiple-band nature of the topological insulator. In addition, it is also found that these behaviors are not sensitive to the gap parameter of the two-dimensional topological insulator model. Our study suggests that the electron density manipulation via electrical gating in a two-dimensional topological insulator is less effective and more delicate than that in a traditional single-band semiconductor.
The optical response of an inverted InAs/GaSb quantum well is studied theoretically. The influence of an in-plane magnetic field that is applied parallel to the quantum well is considered. This in-plane magnetic field will induce a dynamical polarization even when the electric field component of the external optical field is parallel to the quantum well.The electron-electron interaction in the quantum well system will lead to the de-polarization effect. This effect is found to be important and is taken into account in the calculation of the optical response. It is found that the main feature in the frequency dependence of the velocity-velocity correlation function remains when the velocity considered is parallel to the in-plane magnetic field. When the direction of the velocity is perpendicular to the in-plane magnetic field, the depolarization effect will suppress the oscillatory behavior in the corresponding velocity-velocity correlation function. The in-plane magnetic field can change the band structure of the quantum well drastically from a gapped semiconductor to a no-gapped semi-metal, but it is found that the distribution of the velocity matrix elements or the optical transition matrix elements in the wave vector space has the same two-tadpole topology.
