Multiband superconductivity in the topological Kramers nodal-line semimetals

TL;DR

This paper provides experimental and theoretical evidence for multiband superconductivity in topological Kramers nodal-line semimetals NbRuSi and TaRuSi, revealing their unconventional and topological superconducting nature.

Contribution

It demonstrates multiband superconductivity in NbRuSi and TaRuSi through combined muon-spin relaxation, electrical resistivity, specific heat measurements, and band-structure calculations.

Findings

Superconductivity below 3-4 K in NbRuSi and TaRuSi.

Field-dependent relaxation fits a two-band model.

Evidence supports multiband and topological superconductivity.

Abstract

Recent band-structure calculations predict that the ruthenium-based ternary silicides are three-dimensional Kramers nodal line semimetals. Among them, NbRuSi and TaRuSi show bulk superconductivity (SC) below $T_c \sim 3$ K and 4 K, as well as spontaneous magnetic fields. The latter indicates the breaking of time-reversal symmetry and, thus, unconventional SC in both compounds. Previous temperature-dependent muon-spin spectroscopy studies failed to distinguish whether such compounds exhibit single-gap or multi-gap SC. Here, we report on systematic measurements of the field-dependent muon-spin relaxation rates in the superconducting state and on temperature-dependent electrical resistivity and specific heat under applied magnetic fields. Both the upper critical field and the field-dependent superconducting relaxation are well described by a two-band model. By combining our experimental results with numerical band-structure calculations, we provide solid evidence for multiband SC in NbRuSi and TaRuSi, and thus offer further insight into the unconventional- and topological nature of their superconductivity.