Superconducting ground state study of valence skip compound AgSnSe$_2$

TL;DR

This study investigates the superconducting properties of AgSnSe$_2$, revealing two-gap superconductivity and preserved time-reversal symmetry through comprehensive experimental techniques.

Contribution

It provides the first detailed experimental evidence of two-gap superconductivity and time-reversal symmetry preservation in the valence-skipped compound AgSnSe$_2$.

Findings

Evidence of two-gap superconductivity from specific heat and $ ext{H}_{c2}(T)$ measurements.

Confirmation of two-gap behavior via transverse-field $ ext{mu}$SR.

Preservation of time-reversal symmetry in the superconducting state.

Abstract

The valence-skipped superconductors are natural candidates for unconventional superconductivity, as they can exhibit a negative effective, attractive interaction for electron-pairing. This work reports comprehensive XRD, magnetization, specific heat and muon spin rotation and relaxation measurements ($\mu$SR) on a valence-skipped compound: AgSnSe$_2$. The temperature dependence of the electronic specific heat ($C_{el}(T)$) and of the upper critical field ($H_{c2}(T)$) provide evidence of two-gap superconductivity, which is also confirmed by our transverse-field $\mu$SR measurements. Our zero-field $\mu$SR measurements suggest preserved time-reversal symmetry in the superconducting ground state of AgSnSe$_2$.