ULTRASONIC INVESTIGATION OF THERMALLY ASSISTED FLUX FLOW IN (LA1-XSRX)2CUO4 CERAMICS

We measured the change in the ultrasonic attenuation coefficient DELTA-alpha(T, H) and sound velocity DELTA-V(s)(T, H) with temperature T and magnetic field H for (La(1-x)Sr(x))2CuO4 (x = 0.075) ceramic samples. While both DELTA-alpha-(H) and DELTA-V(s)(H) varied proportional-to H(n)(n approximately 1.6) at a temperature T = 4.2 K, no difference was observed in the DELTA-V(s)(H) versus H curves between the cases of H parallel-to K and H perpendicular-to K (K: polarization vector of sound waves), and the theory of Pankert. Furthermore, the plots of alpha(T, 10T)-alpha-(T, 0T) versus T showed a broad peak at T approximately 30 K accompanied by a broad step in the V(s)(T, 10T)-V(s)(T, 0T) versus T curve. Although the peak could be attributed to energy dissipation due to thermally assisted flux flow, the width of the peak was much larger than the prediction of the theory. Here, we adopted the intrinsic pinning model proposed by Tachiki et al. for the explanation of the discrepancies with the theory.