Bi Substitution Effects on Superconductivity of Valence-Skip superconductor AgSnSe2

TL;DR

This study explores how substituting Bi for Sn in AgSnSe2 affects its superconductivity, revealing a slight increase in transition temperature and indicating valence-skip states may not promote superconductivity.

Contribution

It demonstrates that partial Bi substitution enhances Tc in AgSnSe2 and challenges the assumption that valence-skip states support superconductivity in this system.

Findings

Superconducting Tc increased from 4.5 K to 5.0 K with Bi substitution.

Bi substitution was successful up to x=0.2, with insulating phase appearing above x=0.3.

Valence-skip states of Sn are not positively linked to superconductivity in AgSnSe2.

Abstract

We have synthesized AgSn1-xBixSe2 polycrystalline samples to investigate the effect of partial substitution of mixed-valence Sn by Bi3+ to the superconductivity of the valence-skip superconductor AgSnSe2. The Bi-substituted AgSn1-xBixSe2 were obtained up to x = 0.2, but an insulating phase Ag2SnBi2Se5 with a NaCl-type structure showed up above x = 0.3. The superconducting transition temperature increased from 4.5 K (x = 0) to 5.0 K (x = 0.1) by Bi substitution. The enhancement of superconductivity by the suppression of the valence-skip states of Sn suggests that the valence-skip states of Sn are not positively linked to the pairing mechanisms of superconductivity in the AgSnSe2 system.