Singlet-triplet mixing in the order parameter of the noncentrosymmetric superconductor Ru$_{7}$B$_{3}$

TL;DR

This study investigates the superconducting gap structure of Ru$_7$B$_3$, a noncentrosymmetric superconductor, providing experimental evidence for the predicted mixing of singlet and triplet order parameters due to broken inversion symmetry.

Contribution

The paper presents the first experimental confirmation of singlet-triplet mixing in Ru$_7$B$_3$ using small-angle neutron diffraction, supporting theoretical models of noncentrosymmetric superconductors.

Findings

Evidence of mixed singlet-triplet gap from vortex lattice measurements

Temperature dependence matches models of broken inversion symmetry

Confirms theoretical predictions of order parameter mixing

Abstract

One of the key effects which is predicted to arise in superconductors without a centre of inversion is the mixing of singlet and triplet order parameters, which are no longer good quantum numbers on their own due to parity. We have probed the gap structure in the noncentrosymmetric superconductor Ru$_7$B$_3$, through small-angle neutron diffraction from the vortex lattice, in order to search for the proposed mixed order parameter. We find that the measured temperature dependence of the vortex-lattice form factor is well characterised by a model constructed to describe the effects of broken inversion symmetry on the superconducting state, indicating the presence of a mixed singlet-triplet gap and confirming the theoretical predictions.