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

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 ($\hat{I}¼$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 $\hat{I}¼$SR measurements. Our zero-field $\hat{I}¼$SR measurements suggest preserved time-reversal symmetry in the superconducting ground state of AgSnSe${}_2$.

8 pages, 6 figures