Nodal gap structure in the noncentrosymmetric superconductor LaNiC2 from magnetic-penetration-depth measurements

TL;DR

This study investigates the superconducting gap structure of LaNiC2 using magnetic-penetration-depth measurements, revealing evidence of nodal gaps and highlighting the importance of sample quality in interpreting superconducting properties.

Contribution

First direct measurement of the temperature dependence of magnetic penetration depth in LaNiC2 showing nodal gap structure, clarifying previous conflicting results.

Findings

T^2 dependence of penetration depth below 0.4Tc indicating nodal gaps

Sample quality affects interpretation of superconducting gap symmetry

No magnetic phases observed in LaNiC2

Abstract

We report measurements of the temperature dependence of the magnetic penetration depth in different quality polycrystalline samples of noncentrosymmetric LaNiC2 down to 0.05 K. This compound has no magnetic phases and breaks time-reversal symmetry. In our highest quality sample we observe a T^2 dependence below 0.4Tc indicative of nodes in the energy gap. We argue that previous results suggesting conventional s-wave behavior may have been affected by magnetic impurities.