Highly effective and isotropic pinning in epitaxial Fe(Se,Te) thin films grown on CaF2 substrates

TL;DR

This paper demonstrates that epitaxial Fe(Se,Te) thin films grown on CaF2 substrates exhibit highly effective, isotropic vortex pinning, leading to high critical current densities with minimal magnetic field dependence.

Contribution

The study reveals that nanoscale lattice disorder in Fe(Se,Te) films on CaF2 causes isotropic pinning, contrasting with anisotropic pinning in other substrates.

Findings

Critical current density exceeds 1 MA/cm2 in self field

Pinning is isotropic and weakly dependent on magnetic field

Defects at 5-20 nm scale are responsible for isotropic pinning

Abstract

We report on the isotropic pinning obtained in epitaxial Fe(Se,Te) thin films grown on CaF2 (001) substrate. High critical current density values larger than 1 MA/cm2 in self field in liquid helium are reached together with a very weak dependence on the magnetic field and a complete isotropy. Analysis through Transmission Electron Microscopy evidences the presence of defects looking like lattice disorder at a very small scale, between 5 and 20 nm, which are thought to be responsible for such isotropic behavior in contrast to what observed on SrTiO3, where defects parallel to the c-axis enhance pinning in that direction