In a quasi-two-dimensional (2D) electron system under an in-plane magnetic field, we have observed extrema in characteristics of intersubband excitations when a certain resonance condition is imposed on the magnetic field and momentum of the excitations. By changing the mutual alignment of the magnetic field and momentum, we have shown that the dispersion of the intersubband excitations in the in-plane magnetic field has a strong rotational anisotropy. The anisotropic contribution to the energy due to the quasi-2D electron system asymmetry is found to be a linear function of the magnetic field and in-plane momentum and can be used as an efficient tool in measuring the asymmetry of the 2D confining potential.

• Received 21 September 1999

DOI:https://doi.org/10.1103/PhysRevB.61.1712