Zero sound experiments on the distorted b phase and in the BA transition region at low pressures

Abstract

Zero sound at 8.9 and 26.8 MHz, propagating parallel with the magnetic field, shows an attenuationmaximumalongtheTB A line in a field of∼ 2 kG at low pressures. This is in accordance with the theoretical prediction that a critical magnetic field separates two types of B phases, with and without nodes in the energy gap at the transition line. The B → A phase change takes place via an intermediate state, with excess sound attenuation both at 8.9 and 26.8 MHz.