Bulk superconductivity in La2O2M4S6-type layered oxychalcogenide La2O2Bi3Ag0.6Sn0.4S5.7Se0.3

TL;DR

This study enhances the superconducting transition temperature in layered oxychalcogenides through element substitutions, achieving bulk superconductivity with Tc up to 3.0 K in La2O2Bi3Ag0.6Sn0.4S5.7Se0.3.

Contribution

It introduces a new method of increasing Tc in La2O2M4S6-type materials via Sn and Se substitutions, demonstrating improved bulk superconductivity.

Findings

Tc increased to 2.3 K with Sn substitution.

Bulk superconductivity with Tc of 3.0 K achieved with combined Sn and Se substitutions.

Superconducting volume fraction improved with element substitutions.

Abstract

Recently, we reported the observation of superconductivity at ~0.5 K in a La2O2M4S6-type (M: metal) layered oxychalcogenide La2O2Bi3AgS6, which is a layered compound related to the BiS2-based superconductor system but possesses a thicker Bi3AgS6-type conducting layer. In this study, we have developed the La2O2Bi3AgS6-type materials by element substitutions to increase the transition temperature (Tc) and to induce bulk nature of superconductivity. A resistivity anomaly observed at 180 K in La2O2Bi3AgS6 was systematically suppressed by Sn substitution for the Ag site. By the Sn substitution, Tc increased, and the shielding volume fraction estimated from magnetization measurements also increased. The highest Tc (= 2.3 K) and the highest shielding volume fraction (~20%) was observed for La2O2Bi3Ag0.6Sn0.4S6. The superconducting properties were further improved by Se substitutions for the S site. By the combinational substitutions of Sn and Se, bulk-superconducting phase of La2O2Bi3Ag0.6Sn0.4S5.7Se0.3 with a Tc of 3.0 K (Tconset = 3.6 K) was obtained.