Enhancement of the Superconducting Transition Temperature in FeSe Epitaxial Thin Films by Anisotropic Compression

TL;DR

This study demonstrates that applying anisotropic in-plane strain to FeSe thin films significantly enhances their superconducting transition temperature, surpassing bulk values and suggesting new avenues for superconductor applications.

Contribution

It reveals that epitaxial strain on FeSe thin films can increase $T_c$, providing a novel method to improve Fe-based superconductor performance.

Findings

Superconducting $T_c$ reached 11.4 K in strained FeSe films.

$T_c$ enhancement is due to in-plane anisotropic compression.

$T_c$ is weakly dependent on the $c/a$ lattice ratio.

Abstract

In order to investigate the effects of in-plane strain on the superconductivity of FeSe, epitaxial thin films of FeSe were fabricated on CaF$_2$ substrates. The films are compressed along the a-axis and their superconducting transition temperatures $T_{\mathrm c}^{\mathrm {zero}}$ reach 11.4 K, which is approximately 1.5 times higher than that of bulk crystals. The $T_{\mathrm c}$ values are weakly dependent on the ratio of the lattice constants, $c$ / $a$, compared to that of Fe(Se,Te). Our results indicate that even a binary system FeSe has room for improvement, and will open a new route for the application of Fe-based superconductors.