Hg,Re-1223 system: Tc dependence on hydrostatic pressure and thermopower measurements

Samples of Hg 1− x Re x Ba 2Ca 2Cu 3O 8+ δ superconductor (Hg,Re-1223) were prepared with varying rhenium (Re) nominal content (0.15⩽ x⩽0.20) in order to study the changes on the critical temperature under external hydrostatic pressure. At low pressures the ∂ T c/∂ P depends strongly on the Re doping and the sample with x=0.18 shows the largest measured value. However, thermopower measurements reveal that there is no significant change in the numbers of carriers for the different Re content (0.15⩽ x⩽0.20) meaning that ∂ T c/∂ n is the same for all samples which, in principle, have an optimal oxygen content. Taking into account that d T c/d P=∂ T c i/∂ P+[∂ T c/∂ n][∂ n/∂ P] and ∂ T c/∂ n does not depend on the Re content we can argue that the intrinsic term (∂ T c i/∂ P) determines the influence of external hydrostatic pressure on T c.