Quantum oscillations of microwave helicon dispersion in n-type InSb and InAs

The effect of orbital quantization on microwave helicon dispersion in n type InSb and InAs is investigated theoretically and experimentally. In the local limit, the leading term describing helicon dispersion is, unlike helicon damping, unaffected by orbital quantization. Quantum effects enter through the scattering-dependent terms involved in the dispersive part of the helicon propagation constant. The main contribution is shown to be associated with the Shubnikov-de Haas-like oscillations of the scattering correction to the dissipationless Hall conductivity. Experimental measurements of the transmitted helicon phase observed at quantizing magnetic fields in highly doped n-type InSb and InAs at 35 GHz and liquid-helium temperature are compared with the theory. The magnetic field dependence of the observed oscillations in helicon phase agrees reasonably well with the theoretical analysis. While little can be said analytically about the amplitude of these oscillations (of the order of a few percent), our data does provide an empirical measure of the limits within which the usual classical analysis of helicon dispersion is valid. Finally, the effect of quantum oscillations appears to be considerably stronger in the helicon dispersion than in the related de problem of the Hall coefficient.