Abstract
In the last decade, the self-field critical current density J(c)(s.f.) in Type-II superconductors has been considered fundamentally limited by a Silsbee-like criterion of J(c)(s.f.) = H(c1)/λ. We show that this universal limit to self-field critical current density J(c)(s.f.) is not universally valid. We present several examples for this in YBa(2)Cu(3)O(7-δ)-type and REBa(2)Cu(3)O(7-δ) thin films and one for Nb thin films and show that calculated J(c)(s.f.) using the Silsbee-like criterion using thermodynamic parameters has been substantially exceeded experimentally. We also show that J(c)(s.f.) can be significantly improved by incorporation of artificial pinning centers (APCs), further implying that no such universal limit to J(c)(s.f.) can exist because such an upper bound, J(c)(s.f.) would have to be independent of APCs. These findings call for a revision of the accepted understanding of current-carrying limits in Type-II superconductors and reveal substantial potential for improving J(c) in REBCO-based coated conductors through optimization of APCs for large-scale applications, including commercial nuclear fusion.