Nonlinear response of type II superconductors: A new method of measuring the pressure dependence of the transition temperature Tc(P)

A technique of measuring Tc(P) in the diamond anvil cell by the third harmonic of the ac susceptibility (V3f) is described. It requires no background subtraction and allows the use of gasket materials made from hardened steels. In addition, the observed peak structure in the V3f vs T data allows regions with different critical temperatures to be distinguished. Results for single crystals (with typical size, 0.25 mm×0.25 mm×0.1 mm) of the Tl2Ba2CuO6+δ and YBa2Cu3O7−δ systems are presented. The effects of sample inhomogeneities and nonhydrostatic conditions are discussed.