Magnetoacoustic quantum oscillations

The electronic structure of rare-earth atoms with the configuration (Xe)4f"5d 6s gives rise to conduction bands with 5d and 6s character in the intermetallic compounds. The d bands can have a rather large density of states. Therefore the coupling of phonons to these itinerant electrons can be quite strong. In this chapter we review experimental effects caused by the interaction of conduction electrons with sound waves. These experiments mainly concern the anomalous temperature dependence of symmetry elastic constants and the presence of magnetoacoustic quantum oscillations observed in sound velocity and attenuation. 

We first introduce the concept of deformation potential coupling which is applied to calculate the temperature dependence of elastic constants, followed by a presentation and discussion of relevant experimental data. Afterwards we shall present examples for magnetoacoustic quantum oscillations in rare-earth inter-metallics. 

Magnetoacoustic quantum oscillations have been observed in this compound for the Cji mode (Liithi et al. 1984) and for the C44, and the Cjj - Cjj modes (Suzuki et al. 1985a, Ewert et al. 1987). The observed frequencies are very small, however, typically F 5-6 T. They arise from tiny flat electron ellipsoids within the necks along the [110] directions in the simple cubic Brillouin zone (Suzuki et al. 1985a, Onuki et al. 1988). Until now, higher frequencies have not been observed in MAQO techniques. 

Magnetoacoustic quantum oscillations were obtained for LaAg (Niksch et al. 1987). Two kinds of ellipsoidal Fermi surfaces, denoted by a and ji, were observed, as shown in fig. 17. The solid lines are theoretical ones based on relativistic self-consistent Augmented Spherical Wave (ASW) calculations. 

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