Evidence of Nodal Line in the Superconducting Gap Symmetry of Noncentrosymmetric ThCoC${}_2$

Abstract

The newly discovered noncentrosymmetric superconductor ThCoC${}_2$ exhibits numerous unconventional behavior in the field dependent heat capacity data. Here we present the first measurement of the gap symmetry of ThCoC${}_2$ by muon spin rotation/relaxation $(\mu$SR) measurements. Temperature dependence of the magnetic penetration depth measured using the transverse field $\mu$SR measurement reveal the evidence of nodal pairing symmetry. To understand these findings, we carry out the calculations of superconducting pairing eigenvalue and eigenfunction symmetry due to the spin-fluctuation mechanism, by directly implemented the {\it ab-initio} band structures. We find that the system possesses a single Fermi surface with considerable three-dimensionality, and hence a strong nesting along the $k_z$-direction. Such a nesting promotes a superconducting pairing with a $\cos k_z$-like symmetry with a prominent nodal line on the $k_z=\pm \pi /2$ plane. The result agrees well with the experimental data.

3 pages, 5 figures