Niobium Fermi surface and the magnetoacoustic interaction: Polarization selectivity

The magnetoacoustic interaction for field →H normal to propagation vector →q has been studied in high-purity niobium at frequencies extending to 650 and 430 MHz for longitudinal and transverse waves, respectively. Fermi-surface calipers determined for →q∥[100] and →ε∥[010] agree within about 2% with the augmented-plane-wave theoretical values for the distorted ellipsoids. Also, an interesting and useful "caliper-selectivity" mechanism operative in the transverse-wave case was observed which, for particular orientations of wave polarization →ε, served to isolate individual calipers so that the calipers corresponding to a single Fermi sheet were swept out as →H was rotated through 360^∘{}. The corresponding presence of a single period in the oscillations at all field angles permitted relaxation of the number of oscillations required for precise determination of the electron momenta.