Application of Gas Lasers to High-Resolution Magnetospectroscopy

Abstract

The study of oscillatory interband magnetoreflection spectra has yielded much information on the energy band structure of semiconductors and semimetals. The oscillations in reflectivity, normally measured as a function of magnetic field at constant photon energies in the infrared, are associated with direct transitions from Landau levels in the valence band to Landau levels in the conduction band. In the limit of very small electronic losses both the top of valence Landau levels and the bottom of conduction Landau levels have singularly high densities of states, and the interband transition has a sharp cutoff at a critical magnetic field at which the minimum separation between the paired levels equals the photon energy. The cutoff causes a discontinuity in the reflectivity, thus making the so-called oscillatory spectra a series of reflectivity breaks occurring at each critical field for different pairs of states (1). Indeed, one observes such spectra on recently available high-purity single crystals of bismuth at liquid helium temperature. The spectroscopic measurements of this resonant phenomenon will require, in addition to homogeneous magnetic fields, a high degree of monochro-maticity in the infrared, which may exceed the conventional capacity of dispersive spectrometers.