Internal friction and smearing of superconducting gap structures in high-T<inf>c</inf>superconductors

Abstract

For both BiSrCaCuO and TlBaCaCuO samples, the internal frictions, Q -1 , in the kHz range reveal a plateau, Q -1 p , above T c and drop rapidly below T c with the turning points located just at T c for various samples with different T c values. This kind o f anomaly cannot be observed for non-superconducting samples. The drop of Q -1 p below T c is found to be closely related to supercondu cting condensation. The existence of Q -1 p for high-T c superconductors can be reasonably explained using the coupling-model among carriers with local dynamic distortion. Further, taking into account the smearing of the superconducting gap structure resulting from the recombination of quasi-particles and by modifying the BCS relative jump rate as S(E, E′, Γ)=Re [1-Δ 2 / (E-iΓ)(E′-iΓ)], the calculated results of the internal friction below T c are in fair agreement with the experimental data. The superconducting gap, Δ, and the damping rate, Γ, for both BiSrCaCuO and TlBaCaCuO have also been obtained. These values are in accordance with those obtained by tunneling spectrum and NMR methods, etc. © 1993.