Effective Mass Anisotropy of [Formula presented] Electrons in [Formula presented] Quantum Wells

Resonant magnetotunneling in [Formula presented] double barrier structures is used to demonstrate that the effective mass of confined [Formula presented] conduction electrons becomes anisotropic when an electric field is applied perpendicular to the interfaces. Although several authors have previously reported [Formula presented]-related optical anisotropy, this is the first example of a corresponding electrical anisotropy. The results are explained using a quantum mechanical model involving interface band mixing that contains additional features not found in the optical case.