Ultrasonic Attenuation in URu₂Si₂

Abstract

The ultrasonic attenuation and the sound velocity were measured on a single crystal of URu 2 Sr 2 at frequencies up to 285 MHz. The sound velocity increases with decreasing temperature and shows a kink anomaly at T N =17.55 K, while the attenuation shows a step increase and takes a peak value at T N . Although the transition temperature T N , is independent of magnetic filed perpendicular to the c-axis, it quadratically decreases with increasing magnetic field H parallel to the c-axis (the magnetic easy axis), that is, T N (H)-T N (0)=-aH 2 where a = 12 mK/T 2 . The attenuation takes a broad peak at the superconducting transition temperature T c =1.20 K. Instead of the exponential BCS behavior, T 3 dependence of th attenuation temperature observed at T≪T c .