Evidence for two-gap superconductivity in the non-centrosymmetric compound LaNiC$_2$

Abstract

We study the superconducting properties of the non-centrosymmetric compound LaNiC$_2$ by measuring the London penetration depth $Δλ(T)$, the specific heat $C(T,B)$ and the electrical resistivity $ρ(T,B)$. Both $Δλ(T)$ and the electronic specific heat $C_e(T)$ exhibit exponential behavior at low temperatures and can be described in terms of a phenomenological two-gap BCS model. The residual Sommerfeld coefficient in the superconducting state, $γ_0(B)$, shows a fast increase at low fields and then an eventual saturation with increasing magnetic field. A pronounced upturn curvature is observed in the upper critical field $B_{c2}(T)$ near $T_{c}$. All the experimental observations support the existence of two-gap superconductivity in LaNiC$_2$.

8 pages, 8 figures