Photoacoustic detection of the superconducting transition in high <i>T</i> <i>c</i> superconductors

Abstract

Photoacoustic measurements for polycrystalline samples of orthorhombic YBa2Cu3O7−x, GdBa2Cu3O7−x, and DyBa2Cu3O7−x have been carried out in the range of temperatures between 85 and 100 K. An anomalous change of photoacoustic signal due to the specific heat anomaly of the superconductor at transition temperature has been observed. The temperature at which the photoacoustic signal intensity changes anomalously has been found to correspond to the offset temperature of superconducting transition in resistivity measurement. The changes of photoacoustic signal have been analyzed using Rosencwaig and Gersho’s theory [J. Appl. Phys. 47, 64 (1976)]. The superconducting transition of the samples was, from the photoacoustic measurements, found to be a second-order transition with no latent heat.