Doping-induced superconductivity in the topological semimetal Mo5Si3

TL;DR

This study discovers Re-doped Mo5Si3 as a new topological superconductor with increasing Tc up to 5.78 K, revealing a link between doping, electron-phonon coupling, and nontrivial band topology.

Contribution

It reports the first doping-induced superconductivity in a topological semimetal Mo5Si3, demonstrating tunable Tc and nontrivial band topology.

Findings

Superconductivity appears with Re doping in Mo5Si3.

Tc increases from 1.67 K to 5.78 K with doping.

Band structure shows nontrivial topology with Re doping.

Abstract

Chemical doping of topological materials may provide a possible route for realizing topological superconductivity. However, all such cases known so far are based on chalcogenides. Here we report the discovery of superconductivity induced by Re doping in the topological semimetal Mo$_{5}$Si$_{3}$ with a tetragonal structure. Partial substitution of Re for Mo in Mo$_{5-x}$Re$_{x}$Si$_{3}$ results in an anisotropic shrinkage of the unit cell up to the solubility limit of approximately $x$ = 2. Over a wide doping range (0.5 $\leq$ $x$ $\leq$ 2), these silicides are found to be weakly coupled superconductors with a fully isotropic gap. $T_{\rm c}$ increases monotonically with $x$ from 1.67 K to 5.78 K, the latter of which is the highest among superconductors of the same structural type. This trend in $T_{\rm c}$ correlates well with the variation of the number of valence electrons, and is mainly ascribed to the enhancement of electron-phonon coupling. In addition, band structure calculations reveal that superconducting Mo$_{5-x}$Re$_{x}$Si$_{3}$ exhibits nontrivial band topology characterized by $Z_{2}$ invariants (1;000) or (1;111) depending on the Re doping level. Our results suggest that transition metal silicides are a fertile ground for the exploration of candidate topological superconductors.