Comparative analysis of specific heat of YNi2 B2 C using nodal and two-gap models

The magnetic field dependence of low temperature specific heat in YNi2 B2 C was measured and analyzed using various pairing order parameters. At a zero magnetic field, the two-gap model, which has been successfully applied to MgB2 and the point-node model, appear to describe the superconducting gap function of YNi2 B2 C better than other models based on the isotropic s -wave, the d -wave line nodes, or the s+g wave. The two energy gaps, ΔL =2.67 meV and ΔS =1.19 meV, are obtained. The observed nonlinear field dependence of the electronic specific heat coefficient, γ(H)∼ H0.47, is quantitatively close to the γ(H)∼ H0.5 expected for nodal superconductivity or that can be qualitatively explained using a two-gap scenario. Furthermore, the positive curvature in Hc2 (T) near Tc is qualitatively similar to that in the other two-gap superconductor MgB2.