Electron spin resonance in InSb under uniaxial stress

Abstract

Intraband magnetooptical experiments have been successfully used to determine band parameters of semiconductors. In particular, in narrow gap semiconductors the influence of the interaction of e.g. the conduction band with other bands can be studied. This interaction leads to a mixing of electronic states. The application of uniaxial stress can induce an additional strain interaction. The magnetooptical transition between the Landau subbands 0 + and O-, the spin resonance (SR), is particularly sensitive to these interactions. The conduction band-valence-band interaction causes the nonparabolicity of the bands. The Landau subband wavefunctions 0 +, Oare a mixture of conduction and valence band states and are not spin eigenstates. However the electric dipole spin resonance matrix element is proportional to k;l and = 0 [I]. In high magnetic fields, magnetic freeze-out causes the matrix element to be very small because of its klt dependence. In crystals like InSb, as a consequence of the inversion asymmetr~ two additional terms appear in the conduction band energy dispersion relation: (I) k 3 terms due to the interaction with higher bands (strength determined by the constant B) and (2) in uniaxially stressed crystals, k linear terms due to the strain interaction between conduction and valence band (constant C2) . This means that the inversion asymmetry leads to an additional mixing of the O + and Ostates and thus to an enhancement of the matrix element . Experimentally, this effect could be observed in a SR photoconductivity experiment [3]. It was explained in terms of a six band model taking into account the reduced symmetry of the stressed crystal. With transmission experiments [4] we determined the absorption coefficient and the deformation potential C 2 which governs the strength of the stress enhanced spin resonance. In this paper, we present an experimental study using Fourier transform and laser spectroscopy as well as a theoretical treatment of the problem based on an exact solution of the eight band model (conduction band, valence band, split off band) with higher bands included by perturbation theory. We also discuss the consequences for the interpretation of other experiments, i.e. Shubnikov-de Haas and [5], magnetophonon [6] and intra-valence-band magnetooptical experiment [7].