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

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.]