Magnetoacoustic Absorption and the Fermi Surface in Potassium

Magnetoacoustic measurements in zone-refined and oriented single crystals of potassium have yielded detailed information on the relative attenuation, the Fermi surface, and the phase factors in this metal for magnetic-field directions lying near the 100>, 110>, and 112> axes. The longitudinal ultrasonic wave was propagated along the 110> axis, perpendicular to the magnetic field. The data show that the Fermi surface in potassium is only slightly distorted relative to its free-electron value, bulging by about 0.3% in the 110> direction and pushed in by about 0.4 and 0.5%, respectively, in the 100> and 111> directions. The deviation in kf from the average value, kf=(7.44±0.06)×10⁷ cm^-1, is found to be about 0.8%. The average value of the phase factor for potassium is found to lie rather close to the free-electron value of 0.375.