Magnetic Subband Structure ofα−Sn

The energies of the magnetic subbands associated with one conduction band and two valence bands of $\alpha -\mathrm{Sn}$ are calculated as a function of $k_z$, where $k_z$ is the wave-vector component in the direction of the magnetic field which is along a cubic axis. Based on the calculated eigenvalues and eigenfunctions, we have evaluated the imaginary part of the interband dielectric constant, which is related to the optical absorption spectrum, for a typical magnetic field strength. A quantum effect due to the degenerate band edge of $\alpha -\mathrm{Sn}$ shows up in the calculated absorption spectrum.