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

We study the superconducting properties of the non-centrosymmetric compound LaNiC${}_2$ by measuring the London penetration depth $\mathrm{\Delta }\lambda (T)$, the specific heat $C(T,B)$ and the electrical resistivity $\rho (T,B)$. Both $\mathrm{\Delta }\lambda (T)$ 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, ${\gamma }_0(B)$, 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${}_2$.