Thermodynamic fluctuation under high pressure in Hg-1223 superconductors

Excess conductivities of polycrystalline Hg-1223 superconductor have been studied under high-pressure conditions. The critical temperature was chosen as the mean field transition temperature Tcmf. Above this temperature, the normal state resistivity decreases with increasing pressure. The relative change in resistivity w.r.t, pressure, namely d In ρ/dp, is about -21% GPa-1. It is much smaller than the typical value of -10% GPa-1 for most high-Tc superconductors. As a consequence of the change in the normal state resistivity due to the applied pressure, the fluctuation-induced conductivity is also changed. The experimental results were analyzed within the framework of Aslamazov-Larkin theory. The logarithmic plots of the excess conductivity versus reduced temperature Ε(Ε = T/Tcmf-1) reveal that there is a cross-over temperature T0 which determines the transition from two- to three-dimensional conductivity of charge carrier transportation. With the help of the cross-over temperature T0, the values of the coherence length for the Hg-1223 superconductor could be estimated. The change in the fluctuation conductivity is discussed in terms of the coherence length and the thermodynamical critical field Hc.