Thermal expansion and velocity of ultrasonic waves in single phase YBa2Cu3O7−x

Abstract We report resistivity, velocity of sound and thermal expansion measurements in single phase YBa 2 Cu 3 O 7−x . With a 94 K superconductivity onset temperature, the velocity shows an increase below T c , while no anomaly in the expansion coefficient was observed at that temperature. The velocity anomaly is larger and of opposite sign to that generally found in conventional superconductors.