Ultrasonic quantum oscillations and the magnetic field dependence of the Fermi energy in semimetallic Bi1-xSbxalloys

Abstract

Ultrasonic quantum oscillations in pure Bi and semimetallic Bi1-xSbx alloys (x=0.012, 0.019, 0.033) have been investigated. Experiments were carried out in the temperature range 1.2-4.2K using longitudinal ultrasonic waves of frequencies up to 90 MHz propagated along the trigonal axis. Magnetic fields between 0.05 and 2.3 T were applied in the yz and xz planes. The angular dependence of the peak positions was studied. The Landau and spin quantum numbers of the oscillation peaks were obtained from the experimentally measured periods and peak positions of the oscillations. The experimental data indicate that, for most orientations of the magnetic field in the yz plane, the magnetic energy levels of electrons in the alloys studied can be described successfully by the ellipsoidal non-parabolic (ENP) model. The magnetic field dependence of the Fermi energy and the carrier density were calculated in the framework of the ENP model for electrons and the parabolic band for holes, using the previously determined band parameters. The magnetic field values at which the electrons in each pocket enter the quantum limit were deduced from the magnetic field dependence of the carrier density. The quantum limit fields obtained from calculations agree with the experimentally predicted values. It is concluded that within the magnetic field range studied the variation of the Fermi energy with magnetic field has a negligible effect on the period of ultrasonic quantum oscillations from light electrons.