Enhanced ultrasonic attenuation of Tl-Ca-Ba-Cu-O at the superconducting transition

Temperature-dependent ultrasonic attenuation measurements have been performed on polycrystalline samples of Tl-Ca-Ba-Cu-O at various frequencies. An attenuation anomaly was observed close to the superconducting transition temperature ${\mathit{T}}_{\mathit{c}}$ (103 K) whose temperature position was frequency independent. The attenuation decreased exponentially with temperature in the superconducting state for both transverse and longitudinal waves. It was also found that the temperature-dependent sound velocity showed a slope change around ${\mathit{T}}_{\mathit{c}}$.