Torsion and electron motion in quantum dots with crystal lattice dislocations

Abstract

The motion of a conducting electron in a quantum dot, with one or several dislocations in the underlying crystal lattice, is considered in the continuum picture, where dislocations are represented by torsion of space. The possible effects of torsion are investigated on the levels of classical motion, on non-relativistic quantum motion, and on spin-torsion coupling terms derivable in the non-relativistic limit of generalizations of the Dirac equation in a space with torsion. Finally, phenomenological spin-torsion couplings analogous to Pauli terms are considered in the non-relativistic equations. Different prescriptions of classical and non-relativistic quantum motion in a space with torsion are shown to give effects that should, in principle, be observable. Semiclassical arguments are presented to show that torsion is not relevant for the classical motion of the centre of a wavepacket. The correct semiclassical limit can instead be described as classical trajectories in a Hamiltonian given by the band energy. In the special case of a spherically symmetric band this motion reduces to straight lines, independently of local crystal orientations. By dimensional analysis the coupling constants of the possible spin-torsion interactions are postulated to be proportional to a combination of the effective mass of the electron, , the lattice constant, a, and . The level splitting is then very small with transition frequencies of the order of 1 kHz, or smaller.