Niobium Fermi surface and the magnetoacoustic interaction: polarization selectivity

The magnetoacoustic interaction for field H⃗ normal to propagation vector q⃗ 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 q⃗∥[100] and ε⃗∥[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 ε⃗, served to isolate individual calipers so that the calipers corresponding to a single Fermi sheet were swept out as H⃗ 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.