Azbel'-Kaner Cyclotron Resonance in Thallium

Abstract

The angular dependence of Azbel'-Kaner cyclotron resonance in single crystals of high-purity thallium has been investigated at 24 GHz and 1.4\ifmmode^\circ\else\textdegree\fi{}K for sample surfaces perpendicular to the three principal crystal-lographic directions. These measurements have revealed sections of Fermi surface not previously reported. Detailed comparisons are made with the nearly free-electron Fermi surface and with Soven's relativistic orthogonalized-plane-wave calculations. While several orbits were observed to be compatible with these models, other orbits were observed which we are unable to assign using either model. Cyclotron resonance for magnetic field directions making oblique angles with a ($10\overline{1}0$) surface has also been investigated. These studies revealed highly anisotropic, large-amplitude resonances for magnetic field directions making angles of up to 80\ifmmode^\circ\else\textdegree\fi{} with the sample surface. These resonances have been attributed to extended orbits that are possible because of magnetic breakdown effects. The extended-orbit mechanism proposed by Khaikin and Cheremisin was found to account qualitatively for the observed behavior. The experimentally determined masses were quantitatively compared with the nearly free-electron predictions, resulting in estimates of the mass enhancement factors ranging from 1.4 to 1.8. These values were found to disagree with the most recent determinations of the specification-heat mass enhancement factor.