Tuning critical field, critical current, and diode effect of narrow thin-film superconductors through engineering inhomogeneous Pearl length

Abstract

We explore critical field and critical current behavior in inhomogeneous narrow thin-film superconducting strips. Formulations are developed to calculate free energy, critical field, and critical current for strips with inhomogeneous Pearl length distributions. Our findings show that inhomogeneities, specifically a shorter Pearl length in the middle of the strip, significantly enhance the critical field $B_{c1}$. This has practical implications for achieving complete flux expulsion. While narrow strips have traditionally been considered the most effective approach to improve $B_{c1}$ and eliminate trapped vortices, our results suggest that engineered inhomogeneities offer an alternative method to enhance $B_{c1}$ and improve flux expulsion without reducing strip width, providing greater design flexibility for superconducting devices. Additionally, we find that for the purpose of increasing the critical current, utilizing an inhomogeneous film with a reduced Pearl length in the middle of the strip is more advantageous. The enhancement in critical current arises from the current suppression effect at the edges induced by the inhomogeneous distribution of superfluid density. Furthermore, we demonstrate that an inhomogeneous film with a left-right asymmetric Pearl length distribution enables control over the nonreciprocity of the critical current, highlighting the potential of engineering inhomogeneous Pearl length distributions to implement devices exhibiting the superconducting diode effect. Our results provide concrete examples of how manipulating the inhomogeneity of Pearl length can enhance the performance of superconducting devices. Various methods such as doping nonuniform impurities or creating a temperature gradient can be employed to implement an inhomogeneous Pearl length distribution.