Distribution of the superconducting gap in an YNi2B2C film studied by point contact spectroscopy

TL;DR

This study uses point contact spectroscopy to analyze the distribution of the superconducting gap in YNi2B2C films, revealing a range of gap values likely due to anisotropy or multiband effects rather than nodes.

Contribution

It provides the first detailed measurement of the gap distribution in YNi2B2C films and discusses its implications for the superconducting pairing mechanism.

Findings

Superconducting gap ranges from 1.5 to 2.4 meV.

The maximum gap ratio 2Δ/kBTc is approximately 3.66.

The temperature dependence of the gap follows BCS theory.

Abstract

The differential resistances $R_d=dV/dI(V)$ of point contacts between a normal metal and a c axis oriented YNi2B2C film ($T_c$ = 15.2K) in the superconducting (SC) state have been investigated. $R_d(V)$ contains clear "gap" features connected with processes of Andreev reflection at the boundary between normal metal and superconductor that allow the determination of the SC gap $\Delta$ and its temperature and magnetic field dependence. A distribution of $\Delta$ from $\Delta_min\approx$ 1.5 meV to $\Delta_max\approx$ 2.4 meV is revealed; however the critical temperature $T_c$ in all cases corresponded to that of the film. The value 2$\Delta_max/k_BT_c\approx$3.66 is close to the BCS value of 3.52, and the temperature dependence $\Delta(T)$ is BCS-like, irrespective of the actual $\Delta$ value. It is supposed that the distribution of $\Delta$ can be attributed to a gap anisotropy or to a multiband nature of the SC state in YNi2B2C, rather than to the presence of nodes in the gap.