Ultrasonic Attenuation in Thallium

Abstract

We have observed both geometric and open-orbit resonances in the ultrasonic attenuation in thallium at frequencies up to 460 Mc/sec. Sound was propagated in the [0001], [11¯20], and [10¯10] directions and extremal k vectors in the planes perpendicular to these propagation directions were measured. The measured k vectors agree well with the calculated values of Soven for the major pieces of the Fermi surface. We also observed an open-orbit resonance and several subharmonics for $\hat{q}$ parallel to [0001] and $\hat{H}$ parallel to [11¯20]. This results from magnetic breakdown between zones 3 and 4 in the vicinity of the $\mathrm{AL}$ line. No open orbits along the $c$ axis were observed, probably indicating that the fourth-zone electron surface does not contact the $\mathrm{ALH}$ plane.