# Limit to Self-Field Critical Current Density in Thin-Film, Type-II Superconductors

## TL;DR

This paper challenges the belief that a specific limit exists for current density in certain superconductors and shows that adding artificial pinning centers can significantly improve performance.

## Contribution

The paper demonstrates that the self-field critical current density in Type-II superconductors is not universally limited by a Silsbee-like criterion.

## Key findings

- Calculated self-field critical current density using the Silsbee-like criterion has been exceeded experimentally in YBa2Cu3O7−δ and REBa2Cu3O7−δ thin films.
- Artificial pinning centers significantly improve self-field critical current density, contradicting the existence of a universal limit.
- Optimization of artificial pinning centers can enhance performance in REBCO-based coated conductors for large-scale applications.

## Abstract

In the last decade, the self-field critical current density Jc(s.f.) in Type-II superconductors has been considered fundamentally limited by a Silsbee-like criterion of Jc(s.f.) = Hc1/λ. We show that this universal limit to self-field critical current density Jc(s.f.) is not universally valid. We present several examples for this in YBa2Cu3O7−δ-type and REBa2Cu3O7−δ thin films and one for Nb thin films and show that calculated Jc(s.f.) using the Silsbee-like criterion using thermodynamic parameters has been substantially exceeded experimentally. We also show that Jc(s.f.) can be significantly improved by incorporation of artificial pinning centers (APCs), further implying that no such universal limit to Jc(s.f.) can exist because such an upper bound, Jc(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 Jc in REBCO-based coated conductors through optimization of APCs for large-scale applications, including commercial nuclear fusion.