An Ultrasonic Study of the Transition hcp-fcc 4He at 1.1 and 1.5 kbar

Abstract

Transverse ultrasonic sound velocity and attenuation at 3 MHz were studied in solid 4He at pressures of 1.1 and 1.5 kbar. The attenuation changed abruptly during the martensitic hcp-fcc transition. The high temperature phase (fcc 4He) had the higher attenuation. Between 8 K and the transition near 15 K the transverse sound velocity decreased up to 7%- an order of magnutude larger than the changes observed in 4He at lower pressures. These changes can be explained by the quasi-harmonic theory.