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 Tc∼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.
@article{arxiv.2506.03509,
title = {Multiband superconductivity in the topological Kramers nodal-line semimetals},
author = {Tian Shang and Jianzhou Zhao and Keqi Xia and Lun-Hui Hu and Yang Xu and Qingfeng Zhan and Dariusz Jakub Gawryluk and Toni Shiroka},
journal= {arXiv preprint arXiv:2506.03509},
year = {2025}
}