Cubic anisotropy of hole Zeeman splitting in semiconductor nanocrystals

Abstract

We study theoretically cubic anisotropy of Zeeman splitting of a hole localized in semiconductor nanocrystal. This anisotropy originates from three contributions: crystallographic cubically-symmetric spin and kinetic energy terms in the bulk Luttinger Hamiltonian and the spatial wave function distribution in a cube-shaped nanocrystal. From symmetry considerations, an effective Zeeman Hamiltonian for the hole lowest even state is introduced, containing a spherically symmetric and a cubically symmetric term. The values of these terms are calculated numerically for spherical and cube-shaped nanocrystals as functions of the Luttinger Hamiltonian parameters. We demonstrate that the cubic shape of the nanocrystal and the cubic anisotropy of hole kinetic energy (so called valence band warping) significantly affect effective $g$ factors of hole states. In both cases, the effect comes from the cubic symmetry of the hole wave functions in zero magnetic field. Estimations for the effective $g$ factor values in several semiconductors with zinc-blende crystal lattices are made. Possible experimental manifestations and potential methods of measurement of the cubic anisotropy of the hole Zeeman splitting are suggested.