Internal friction and ultrasonic attenuation related to carriers in high-Tc superconductors

Abstract

For various samples of Bi-Sr-Ca-Cu-O (2:2:2:3 phase, 2:2:1:2 phase, and 2:2:2:3-2:2:1:2 mixed phases) and Tl-Ba-Ca-Cu-O (2:2:2:3 phase) with different Tc, the internal friction (Q−1) in the kHz range reveals a plateau (Qp−1) above Tc and drops drastically below Tc with the turning point at Tc. This kind of anomaly has not been observed for nonsuperconducting samples. The results of ultrasonic attenuation (α) in Tl-Ba-Ca-Cu-O (2:2:2:3) are similar to that of the internal friction mentioned above. Moreover, it is discovered that the Qp−1 is nearly proportional to Hall carrier density (nH) for Y1−xPrxBa2Cu3O and Gd1−xPrxBa2Cu3O with various Pr content. These results indicate that the drastic drop of Q−1 and α below Tc is caused by superconducting condensation. The energy dissipation (Qp−1 and ap) related to carriers can be explained reasonably by using a coupling model of carriers with local dynamic distortion. Furthermore, by taking into account the smearing of the superconducting gap structure caused by the recombination of quasiparticles and by modifying the BCS relative jump rate as S(E,E’,Γ)=Re{1-Δ2/[(E-iΓ)(E’-iΓ)]}, the calculated results of internal friction and ultrasonic attenuation below Tc agree fairly well with the experimental data. The superconducting gap Δ and the damping rate Γ for both Bi-Sr-Ca-Cu-O and Tl-Ba-Ca-Cu-O have also been obtained and are in accordance with those obtained by tunneling-spectrum, NMR methods, etc.

Source-reported materials — not catalogue approval

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