On the superconducting gap structure of the miassite Rh17S15: Nodal or nodeless?

Recent penetration depth measurement claimed the observation of unconventional superconductivity in the miassite Rh\(_{17}\)S\(_{15}\) single crystals, evidenced by the linear-in-temperature penetration depth at low temperatures, thereby arguing for the presence of the lines of node in its superconducting gap structure. Here we measure the thermal conductivity of Rh\(_{17}\)S\(_{15}\) single crystals down to 110 mK and up to a field of 8 T (\(\simeq 0.4H{\rm_{c2}}\)). In marked contrast to the penetration depth measurement, we observe a negligible residual linear term \(\kappa_0/T\) in zero field, in line with the nodeless gap structure. The field dependence of \(\kappa_0(H)/T\) shows a profile that is more consistent with either a highly anisotropic gap structure or multiple nodeless gaps with significantly different magnitudes. Moreover, first-principles calculations give two electronic bands with complex shape of Fermi surfaces. These results suggest multigap nodeless superconductivity in this multiband Rh\(_{17}\)S\(_{15}\) superconductor.