Microstructural control of the transport properties of $\beta$-FeSe films grown by sputtering

TL;DR

This study explores how structural and growth parameters influence the transport and superconducting properties of sputtered $eta$-FeSe films on SrTiO$_3$, revealing insights into disorder effects, superconductor-insulator transition, and lattice distortion impacts.

Contribution

It provides a detailed analysis of the relationship between film morphology, structural strain, and electronic properties in sputtered $eta$-FeSe films, highlighting the role of lattice distortion.

Findings

Enhanced $T_c$ of ~12 K in textured thick films

High $H_{c2}$ and low anisotropy observed

Structural and morphological evolution during superconductor-insulator transition

Abstract

We have investigated the correlation between structural and transport properties in sputtered $\beta$-FeSe films grown onto SrTiO$_3$ (100). The growth parameters, such as substrate temperature and thickness, have been varied in order to explore different regimes. In the limit of textured thick films, we found promising features like an enhanced $T_{\rm c}\sim12\,$K, a relatively high $H_{\rm c2}$ and a low anisotropy. By performing magnetoresistance and Hall coefficient measurements, we investigate the influence of the disorder associated with the textured morphology on some features attributed to subtle details of the multi-band electronic structure of $\beta$-FeSe. Regarding the superconductor-insulator transition (SIT) induced by reducing the thickness, we found a non-trivial evolution of the structural properties and morphology associated with a strained initial growth and the coalescence of grains. Finally, we discuss the origin of the insulating behavior in high-quality stressed epitaxial thin films. We found that a lattice distortion, described by the Poisson's coefficient associated with the lattice parameters \textit{a} and \textit{c}, may play a key role.