NONLINEAR RESPONSE OF TYPE-II SUPERCONDUCTORS - A NEW METHOD OF MEASURING THE PRESSURE-DEPENDENCE OF THE TRANSITION-TEMPERATURE T-C(P)

A technique of measuring T-c(P) in the diamond anvil cell try the thir d harmonic of the ac susceptibility (V-3f) is described. It requires n o background subtraction and allows the use of gasket materials made f rom hardened steels. In addition, the observed peak structure in the V -3f VS T data allows regions with different critical temperatures to b e distinguished. Results for single crystals (with typical size, 0.25 mmX0.25 mmx0.1 mm) of the Tl2Ba2CuO6+delta and YBa2Cu3O7-delta systems are presented. The effects of sample inhomogeneities and nonhydrostat ic conditions are discussed. (C) 1998 American Institute of Physics.