Depinning Line of High-T_c Superconductor HgBa₂CuO_4+x

Mechanical dissipation of high-T_c superconductor compound HgBa₂CuO_4+x as a function of temperature was measured with the vibrating reed technique. The depinning line determined from the peak temperature of internal friction was found to be higher than that of Bi-based sample but lower than that of Y-based one.