INTERNAL FRICTION AND ULTRASONIC ATTENUATION RELATED TO CARRIERS IN HIGH T_c SUPERCONDUCTORS

For both BiSrCaCuO and TlBaCaCuO samples, internal frictions (Q^-1) in the kHz range reveal a plateau (Q^-1_p) above T_c and a rapid drop below T_c with the turning points located just at T_c for various samples with different T_c. This anomaly cannot be observed in non-superconducting samples. The ultrasonic attenuation (\alpha) in TlBaCaCuO displays similar results to the internal friction. Moreover, it is discovered that the Q^-1_p is nearly proportional to the carrier density for Y(Pr)BaCuO and Gd(Pr)BaCuO with different Pr contents. These results show that the drop of Q^-1 and a below T_c is closely related to superconducting condensation. The Q^-1_p and \alpha_p can be explained using coupling-model of carriers with local dynamic distortion because high T_c superconductors are strong-correlation systems. Furthermore, by taking account of the smearing of superconducting gap structure resulting from the recombination of quasi-particles and by modifying the BCS relative jump rate as S(E, E', \varGamma) = Re1-\Delta²/(E-i\varGamma)(E'-i\varGamma), the calculated results of internal friction and ultrasonic attenuation below T_c are in good agreement with the experimental data. The superconducting gap \Delta and the damping rate \varGamma for both BiSrCaCuO and TlBaCaCuO have also been obtained, they are in accordance with those got by tunneling spectrum and NMR methods, etc.