Spectroscopic evidence of mixed angular momentum symmetry in non-centrosymmetric Ru$_7$B$_3$

TL;DR

This study provides direct spectroscopic evidence of mixed s-wave and p-wave pairing symmetries in non-centrosymmetric Ru$_7$B$_3$, revealing unconventional superconducting order parameters.

Contribution

It is the first direct measurement showing coexistence of singlet and triplet pairing in a non-centrosymmetric superconductor using tunnelling spectroscopy.

Findings

Evidence of both s-wave and p-wave pairing symmetries.

Temperature-dependent variation of singlet and triplet components.

Indications of unconventional pairing mechanisms.

Abstract

Superconducting crystals with lack of inversion symmetry can potentially host unconventional pairing. However, till date, no direct conclusive experimental evidence of such unconventional order parameters in non-centrosymmetric superconductors has been reported. In this paper, through direct measurement of the superconducting energy gap by scanning tunnelling spectroscopy, we report the existence of both $s$-wave (singlet) and $p$-wave (triplet) pairing symmetries in non-centrosymmetric Ru$_7$B$_3$. Our temperature and magnetic field dependent studies also indicate that the relative amplitudes of the singlet and triplet components of the order parameter change differently with temperature.