Zero-bias conductance peak in detached flakes of superconducting 2H-TaS$_2$ probed by scanning tunneling spectroscopy

TL;DR

This study observes a zero bias conductance peak in superconducting 2H-TaS$_2$ flakes, explained by a model involving sign-changing pairing and Andreev states induced by weak scattering at the nodal Fermi surface.

Contribution

It introduces a minimal theoretical model for 2H-TaS$_2$ that explains the zero bias peak via sign-changing pairing and Andreev states, highlighting effects of reduced dimensionality.

Findings

Zero bias conductance peak observed in detached 2H-TaS$_2$ flakes.

Weak scattering at the nodal Fermi surface induces Andreev states.

Dimensional reduction may cause a transition to sign-changing pairing.

Abstract

We report an anomalous tunneling conductance with a zero bias peak in flakes of superconducting 2H-TaS$_2$ detached through mechanical exfoliation. To explain the observed phenomenon, we construct a minimal model for a single unit cell layer of superconducting 2H-TaS$_2$ with a simplified 2D Fermi surface and sign-changing Cooper pair wavefunction induced by Coulomb repulsion. Superconductivity is induced in the central $\Gamma$ pocket, where it becomes nodal. We show that weak scattering at the nodal Fermi surface, produced by non-perturbative coupling between tip and sample, gives Andreev states that lead to a zero bias peak in the tunneling conductance. We suggest that reducing dimensionality down to a few atom thick crystals could drive a crossover from conventional to sign changing pairing in the superconductor 2H-TaS$_2$.