Ultrasonic attenuation and sound velocity changes in a superconducting La 2- xSr xCuO 4 single crystal

Abstract

The ultrasonic attenuation and relative sound velocity measured at frequencies up to 305 MHz in the superconducting state of a La 2- x Sr x CuO 4 single crystal. For longitudinal sound waves propagating along the c-axis, the attenuation increases with increasing temperature with a small peak at 27 K and a large peak at about 37 K. These two peaks, especially the small one, become more obvious at higher frequencies. Simultaneously, the velocity exhibits a jump of about 100 ppm around the superconducting transition. At about 27 K, there is another discontinuity in the sound velocity of about 20 ppm, which corresponds to the small peak in the attenuation measurement.