Pressure-dependent measurements in superconductors

To evaluate the performance of a home-built miniature non-magnetic piston clamp cell we have carried out extensive low-temperature (1.5 to 10 K) measurements of the critical field, Hc, for the element Pb up to a pressure of P = 1.2 GPa. Surprisingly, such data has not previously been reported above 0.3 GPa. From this data the electronic entropy, specific heat, thermal expansion coefficient and compressibility is calculated as a function of temperature, pressure and magnetic field. The zero-field data is consistent with direct thermodynamic measurements and the P-dependence of Tc and specific heat coefficient, γ(T, P), allows the determination of the P-dependence of the pairing interaction. Using Pb as a manometer we investigated the pressure dependence of oxygen isotope effect on Tc for YBa2Cu4O8