Silvanite AuAgTe$_4$: a rare case of gold superconducting material

TL;DR

This study discovers superconductivity in the rare gold-silver mineral AuAgTe$_4$ under pressure, revealing a structural phase transition and providing insights into phonon-mediated superconductivity in gold-containing compounds.

Contribution

It reports the first observation of superconductivity in AuAgTe$_4$ and combines experimental and theoretical analysis to understand its pressure-induced phase transition and superconducting mechanism.

Findings

Superconductivity onset at ~1.5 GPa in AuAgTe$_4$

Structural phase transition at ~5 GPa from monoclinic P2/c to P2/m

Superconductivity likely phonon-mediated with low-energy phonon modes

Abstract

Gold is one of the most inert metals, forming very few compounds, some with rather interesting properties, and only two of them currently known to be superconducting under certain conditions (AuTe$_2$ and SrAuSi$_3$). Compounds of another noble element, Ag, are also relatively rare, and very few of them are superconducting. Finding new superconducting materials containing gold (and silver) is a challenge - especially having in mind that the best high-$T_c$ superconductors at normal conditions are based upon their rather close ''relative'', Cu. Here we report combined X-ray diffraction, Raman, and resistivity measurements, as well as first-principles calculations, to explore the effect of hydrostatic pressure on the properties of the sylvanite mineral, AuAgTe$_4$. Our experimental results, supported by density functional theory, reveal a structural phase transition at $\sim$5 GPa from a monoclinic $P2/c$ to $P2/m$ phase, resulting in almost identical coordinations of Au and Ag ions, with rather uniform interatomic distances. Further, resistivity measurements show the onset of superconductivity at $\sim$1.5 GPa in the $P2/c$ phase, followed by a linear increase of $T_c$ up to the phase transition, with a maximum in the $P2/m$ phase, and a gradual decrease afterwards. Our calculations indicate phonon-mediated superconductivity, with the electron-phonon coupling coming predominantly from the low-energy phonon modes. Thus, along with the discovery of a new superconducting compound of gold/silver, our results advance understanding of the mechanism of the superconductivity in Au-containing compounds, which may pave the way to the discovery of novel ones.