Percolative reconciliation between resistive and magnetic measurements of the transition temperature in HTS thin films

Abstract

Several Bi-Sr-Ca-Cu-O thin films have been produced ex situ by sequential thermal evaporation. Characterizing the transition temperatures Tc of these films, a constant discrepancy between resistive and inductive measurements is observed. The resistive van der Pauw technique indicates Tc (onset) typically above 90 K and Tc (zero) at around 78 K. However, the Tc (onset) for these same films is not seen by an inductive measurement, in which the film surface is in physical contact with a flat spiral coil, inducing changes in the coil inductance during the superconductivity transition. Conversely, the inductive transition starts around 5 K above the resistively obtained Tc (zero). Percolation theory is employed in an attempt to explain this discrepancy and to establish generally how Tc (zero) can be found from the resulting curve in the inductive measurement technique.