INTERNAL FRICTION AND ULTRASONIC ATTENUATION RELATED TO CARRIERS IN HIGH Tc 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', $\varGamma$) = Re{1-$\Delta$²/(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.