Photoacoustic wave propagating from normal into superconductive phases in Pb single crystals

TL;DR

This study investigates photoacoustic wave propagation in Pb single crystals, revealing a MHz-ultrasonic component that is enhanced below the superconducting transition temperature, consistent with BCS theory.

Contribution

It demonstrates the coexistence of thermal and ultrasonic components in photoacoustic waves and their behavior across the superconducting transition in Pb.

Findings

MHz-ultrasonic component is enhanced below T_C

Thermal wave component is unaffected by superconducting transition

Results align with BCS theory predictions

Abstract

Photoacoustic (PA) wave has been examined in a superconductor of the first kind, Pb single crystal. The PA wave is induced by optical excitation of electronic state and propagates from normal into superconductive phases below T$_{\rm C}$. It is clearly shown by wavelet analysis that the measured PA wave includes two different components. The high-frequency component is MHz-ultrasonic and the relative low-frequency one is induced by thermal wave. The latter is observed in a similar manner irrespective of T$_{\rm C}$. On the other hand, the MHz-frequency component is obviously enhanced below T$_{\rm C}$. The behavior is reproduced by the change of attenuation of longitudinal ultrasonic wave and is consistent with BCS theory.