Spectroscopic evidence for two-gap superconductivity in the quasi-one dimensional chalcogenide Nb$_{2}$Pd$_{0.81}$S$_{5}$

TL;DR

This study provides direct spectroscopic evidence for two-gap superconductivity in the quasi-one-dimensional chalcogenide Nb$_{2}$Pd$_{0.81}$S$_{5}$, revealing two distinct superconducting gaps consistent with weak coupling BCS theory.

Contribution

First direct spectroscopic confirmation of two-band superconductivity in Nb$_{2}$Pd$_{0.81}$S$_{5}$, demonstrating its weak coupling two-gap nature.

Findings

Observation of Andreev reflection indicating superconductivity

Identification of two distinct superconducting gaps

Gaps follow BCS temperature and magnetic field evolution

Abstract

We present the first direct evidence for two-band superconductivity in the quasi-one dimensional chalcogenide Nb$_{2}$Pd$_{0.81}$S$_{5}$. Soft point contact spectroscopic measurements reveal Andreev reflection in the differential conductance $G$ in the zero-resistance superconducting (SC) state below $T_c$(=6.6~K). Multiple peaks in $G$ were clearly observed at 1.8~K and were successfully explained by the two-band Blonder-Tinkham-Klapwijk model with two gaps $\Delta_{1}=0.48$~meV and $\Delta_{2}=1.05$~meV. Their evolution in temperature and magnetic field is consistent with the conventional BCS theory. The SC gap to $T_c$ ratio for $\Delta_1$ and $\Delta_2$ is 1.7 and 3.7, which is similar to the weak coupling BCS prediction of 3.5. These results demonstrate that the newly discovered niobium chalcogenide is a two-gap superconductor in the weak coupling limit.