Removal of excess iron by annealing processes and emergence of bulk superconductivity in sulfur-substituted FeTe

TL;DR

This study demonstrates that chemical processing, specifically hydrochloric acid etching and vacuum annealing, enhances bulk superconductivity in sulfur-substituted FeTe by reducing excess iron, as confirmed through physical measurements and magneto-optical imaging.

Contribution

It reveals that chemical treatments can induce and improve bulk superconductivity in S-substituted FeTe by removing excess iron, offering a new route for superconductor development.

Findings

Superconductivity in S-substituted FeTe is enhanced by chemical processing.

Vacuum annealing and acid etching improve superconducting properties.

Superconducting regions are confirmed to be bulk via magneto-optical imaging.

Abstract

There are several strategies to discover new superconductors. Growing new materials and applying high pressures can be the classic ways since superconductivity was found. Also, chemical processing, such as annealing, is another way to induce superconductivity in a non-superconducting material. Here, we show chemical processing effects in the non-superconducting material, sulfur-substituted FeTe. It has been known that superconductivity in S-substituted FeTe is induced by O$_2$ annealing. We revealed that hydrochloric acid etching and vacuum annealing for O$_2$-annealed samples made the quality of superconductivity higher by several physical property measurements. Furthermore, we visualized the superconducting regions by a magneto-optical imaging technique, indicating that the superconductivity in the processed sample was bulk. In this sample, we confirmed that the concentration of excess iron was reduced compared to that in the as-grown state. These results provide an important route to bulk superconductivity in S-substituted FeTe and its related iron-based compounds.