Measurements of ultrasonic attenuation and sound velocity in a single crystal of (La1−xSrx)2CuO4

Abstract

Measurements of the ultrasonic attenuation and sound velocity were made at frequencies of 32 and 87 MHz in a large single crystal of (La0.925Sr0.075)2CuO4 (∼4×4×4 mm3), which exhibits a sharp (ΔT∼1 K) superconducting transition at 37 K. For longitudinal waves propagating along the c axis, the sound velocity shows a sharp softening, Δv/v∼100 ppm, concurrent with the sharp superconducting transition in the susceptibility measurements. Following this transition, the susceptibility exhibits a small tail extending to 27 K, where a smaller softening, Δv/v∼20 ppm, has been observed in the velocity measurements. Accompanying the ∼100-ppm velocity drop, there is a signature in the attenuation; following this feature, the attenuation changes as the temperature is decreased further, with a small kink in the attenuation at 27 K. Additional results of the dependence of the attenuation and sound velocity in external magnetic fields, orientated in the a-b plane, will be presented. [Work supported by ONR.]