Abstract

With an HTS manufacturing business* spun out from our fundamental and applied R&D programmes over the past 27 years, we are particularly conscious of the ongoing need to drive up the critical current density, Jc, and determine its fundamental limits. This talk examines the relationship between thermodynamics and Jc both in the presence and absence of external applied fields. These two limits result in quite different phenomenology. In the self-field limit (Hext = 0) we find that Jc is limited by fundamental parameters and this provides a means to directly measure the London penetration depth, (T), from Jc(T), along with the symmetry and magnitude of the order parameter. The ideas developed are confirmed by the effects of impurity substitution on Jc(T) which have a distinctive character due to the rapid suppression of superfluid density due to impurity scattering. The ideas are also confirmed by applying to 31 different superconducting systems, including s-wave and d-wave, type I and type II. By combining with in-field Jc data we can also extract both the magnitude and T-dependence of the order parameter.