Anomalous ultrasound propagation in the high-Tc superconductors: La1.8Sr0.2CuO4−y and YBa2Cu3O7−δ

Abstract

Attenuation and velocity of longitudinal ultrasound in both known classes of the high-$T_c$ copper-oxide superconductors are found to be highly anomalous compared to conventional superconductors. Attenuation shows a pronounced peak below $T_c$ followed by an approximately power-law decrease at low T. The velocity shows a discontinuity in its temperature derivative at $T_c$ followed by a large increase. The results are inconsistent with dominant contributions from the carriers alone. Anomalies are also observed at higher temperatures suggesting the existence of other phase transitions.