Node-like excitations in superconducting PbMo6S8 probed by scanning tunneling spectroscopy

TL;DR

This study uses scanning tunneling spectroscopy to investigate the superconducting properties of PbMo6S8, revealing evidence of gap nodes and low-energy excitations that challenge conventional s-wave models.

Contribution

First detailed tunneling spectroscopy analysis of PbMo6S8 showing unconventional gap features and evidence of nodal superconductivity.

Findings

Spectra are spatially homogeneous with well-defined coherence peaks.

Data incompatible with conventional isotropic s-wave superconductivity.

Evidence suggests the presence of nodes in the superconducting gap.

Abstract

We present the first scanning tunneling spectroscopy study on the Chevrel phase PbMo6S8, an extreme type II superconductor with a coherence length only slightly larger than in high-Tc cuprates. Tunneling spectra measured on atomically flat terraces are spatially homogeneous and show well-defined coherence peaks. The low-energy spectral weight, the zero bias conductance and the temperature dependence of the gap are incompatible with a conventional isotropic s-wave interpretation, revealing the presence of low-energy excitations in the superconducting state. We show that our data are consistent with the presence of nodes in the superconducting gap.