Evidence of Nodal Line in the Superconducting Gap Symmetry of Noncentrosymmetric ThCoC$_{2}$

TL;DR

This study combines experimental muon spin rotation measurements and ab-initio calculations to reveal nodal line superconductivity in the noncentrosymmetric superconductor ThCoC$_{2}$, highlighting its unconventional pairing symmetry.

Contribution

First combined experimental and theoretical investigation of the gap symmetry in ThCoC$_{2}$, demonstrating nodal line superconductivity due to spin-fluctuation mediated pairing.

Findings

Evidence of nodal pairing symmetry from $ ext{μ}$SR measurements.

Superconducting pairing with $ ext{cos}k_z$-like symmetry due to Fermi surface nesting.

Agreement between experimental data and theoretical calculations.

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.