Intersubband excitations in single-and double-layer electron systems in a parallel magnetic field

Abstract

The spectrum of neutral intersubband excitations in single and double quantum wells has been studied by the inelastic light scattering method. It is shown that excitation energies in an external magnetic field have an anisotropic component proportional to the dipole moment of excitations along the growth axis of the quantum wells. Consequently, the measurement of excitation energy in a magnetic field makes it possible to experimentally estimate the quantitative measure of asymmetry of the quantum wells (dipole moment of the intersubband transition). In addition, a parallel magnetic field makes it possible to considerably extend the range of momenta studied since it shifts the dispersion curves in the momentum space by the value of the anisotropic component. A new method is proposed for determining the symmetry of double quantum wells. In asymmetric wells, intersubband excitations appear between the layers and have a large dipole moment along the growth axis. In symmetric wells, the magnetic field itself induces the dipole moment of intersubband excitations so that the excitation spectrum does not change upon magnetic field inversion. Analysis of energy anisotropy in intersubband excitations in double quantum wells makes it possible to determine the symmetry of double wells to a high degree of accuracy.