Understanding critical currents in superconducting cuprate tapes

One of the key challenges in the fabrication of superconducting coils using cuprate tapes is the parametrization of the critical currents and their dependence on magnetic field, temperature, and angle. Discussions at the Magnet Technology Conference (MT29) in Boston (2025) highlighted the need for standardized characterization and a better understanding of these tapes. Without a shared understanding of the physical phenomena governing critical currents, progress in this area remains difficult. We propose to analyze existing data using a model that explains most observed features. Although the model proposed by P. Mathieu and Y. Simon was published 20 years ago, it remains relatively unknown and certainly unused among engineers in the field, although many physicists were convinced of its validity, a consensus not reflected in the literature. The Mathieu/Simon (MS) model emphasizes the importance of surface pinning mechanisms, which dominate critical currents across a large part of the phase diagram of YBaCuO. Unlike strong and weak pinning mechanisms, which are commonly assumed to be dominant, the MS model accurately predicts the order of magnitude of experimentally measured values, suggesting it should at least be considered the dominant mechanism. The results of calculations based on this model are presented and compared with experimental data, offering directions for the development of new materials.