Depairing critical current density and the vortex-free state in FeSe nanobridges

TL;DR

This study demonstrates that geometric constraints in FeSe nanobridges can achieve the depairing current limit and stabilize a vortex-free state, enhancing critical current density and magnetic field robustness.

Contribution

It provides experimental evidence that geometric constriction in FeSe superconductors induces depairing limit and vortex-free state, advancing understanding of supercurrent physics.

Findings

Critical current density exceeds previous limits in narrow bridges.

Vortex-free state persists under magnetic fields up to 1 kOe.

Geometric constraints enhance lower critical fields.

Abstract

The depairing limit and the vortex-free state in a superconductor is crucial for both the study of supercurrent related physics and the application eliminating noise linked to vortex motion. In this work, we report the evidence of depairing limit and the vortex-free state achieved by geometric constraint in FeSe superconductors. A series of narrow bridges with varying widths at the same location of a single crystal were prepared by the \textquotedblleft pickup\textquotedblright method using successive focused ion beam millings. By simply reducing the width of bridge, the magnitude of critical current density ($J_{\rm{c}}$) is enhanced more than one order, evidence the achievement of depairing limit. Moreover, in the bridge with a width smaller than the penetration depth ($\lambda$), $J_{\rm{c}}$ is found to be robust against magnetic field up to 1 kOe. The field-robust $J_{\rm{c}}$ is a strong piece of evidence for vortex-free state, which is created by the enhancement of lower critical fields due to geometric constraint.