Appearance of the universal value $e^{2}/h$ of the zero-bias conductance in a Weyl semimetal-superconductor junction

TL;DR

This paper demonstrates that a Weyl semimetal-superconductor junction exhibits a universal zero-bias conductance of e^{2}/h per channel, due to topological effects and pairing symmetry, serving as a signature of Weyl fermions.

Contribution

It reveals a universal conductance phenomenon in Weyl semimetal-superconductor junctions arising from topological properties and pairing, independent of material parameters.

Findings

Universal zero-bias conductance of e^{2}/h per channel identified

Conductance signature linked to Weyl fermions and pairing symmetry

Potential experimental signature for time-reversal symmetric Weyl semimetals

Abstract

We study the differential conductance of a time-reversal symmetric Weyl semimetal-superconductor (N-S) junction with an s-wave superconducting state. We find that there exists an extended regime where the zero-bias differential conductance acquires the universal value $e^{2}/h$ per unit channel, independent of the pairing and chemical potentials on each side of the junction, due to a perfect cancellation of Andreev and normal reflection contributions. This universal conductance can be attributed to the interplay of the unique spin/orbital-momentum locking and s-wave pairing that couples Weyl nodes of the same chirality. We expect that the universal conductance can serve as a robust and distinct signature for time-reversal symmetric Weyl fermions, and be observed in the recently discovered time-reversal symmetric Weyl semimetals.