Hybrid Resonance and "Tilted-Orbit" Cyclotron Resonance in Bismuth

Abstract

Measurements have been made of microwave absorption in very pure, single-crystal bismuth as a function of static magnetic field, B at 1.2\ifmmode^\circ\else\textdegree\fi{}K and 70 kMc/sec. The field B was in the plane of the sample along a crystallographic axis; the microwave electric field E was either perpendicular or parallel to B. Except at very low magnetic fields (\ensuremath{\le}100 G), nearly classical skin effect conditions prevail. Onsets of absorption are observed that result from singularities in the effective dielectric coefficient of the bismuth plasma. With E perpendicular to B most of the onsets do not correspond to any previously measured type of single-carrier cyclotron resonance in bismuth, but are hybrid resonances which require the presence of at least two distinct carriers. Such hybrid resonances are associated with longitudinal plasma modes. With E parallel to B, individual carrier cyclotron resonance is observed for those carriers whose cyclotron-orbit planes are tilted with respect to the magnetic field. Such tilts exist when B is not parallel to one of the major axes of the electron energy ellipsoids. A close fit to the experimental data is obtained by a theoretical calculation based on electron and hole masses measured in other experiments.