Far-infrared observation of cyclotron and spin-flip resonances in HgSe

Far-infrared (FIR) magnetotransmission experiments were carried out at 4.2 K on high-purity HgSe crystals, with the use of a C${\mathrm{O}}_2$-pumped FIR laser and magnetic fields up to 14 T. Measurements were performed in the Voigt geometry, at three FIR wavelengths: 96.5, 119, and 163 μm. In addition to the usual plasma-shifted cyclotron resonance occurring in the transverse Voigt geometry, we have observed electric-dipole-excited electron-spin-resonance (EDE-ESR) and combined-resonance transitions. These resonances are made possible by the relaxation of selection rules due to spin-orbit coupling, as a consequence of $\overrightarrow{\mathrm{k}}·\overrightarrow{\mathrm{p}}$ interaction and/or inversion asymmetry. Our data suggest that the inversion-asymmetry mechanism is stronger in HgSe than in other materials studied by FIR magnetotransmission, e.g., InSb. We have also observed a small but unambiguous magnetoplasma shift in EDE-ESR occurring in the transverse Voigt geometry. The positions of the observed resonances at the three laser frequencies were used to obtain band-structure parameters for HgSe within the framework of the Pidgeon-Brown model.