Muon spin rotation/relaxation measurements of the non-centrosymmetric superconductor Mg10Ir19B16

TL;DR

This study investigates the superconducting pairing symmetry in Mg10Ir19B16 using muon spin relaxation and rotation, revealing that sample purity significantly influences the presence of time-reversal symmetry breaking and the superfluid density behavior.

Contribution

It provides the first detailed muon spin measurements on Mg10Ir19B16, showing how sample quality affects superconducting properties and pairing symmetry.

Findings

High purity sample shows no time-reversal symmetry breaking fields.

Superfluid density fits a single-gap BCS model in both samples.

Sample quality impacts the magnitude of superfluid density at zero temperature.

Abstract

We have searched for time-reversal symmetry breaking fields in the non-centrosymmetric superconductor Mg$_{10}$Ir$_{19}$B$_{16}$ via muon spin relaxation in zero applied field, and we measured the temperature dependence of the superfluid density by muon spin rotation in transverse field to investigate the superconducting pairing symmetry in two polycrystalline samples of signficantly different purities. In the high purity sample, we detected no time-reversal symmetry breaking fields greater than 0.05 G. The superfluid density was also found to be exponentially-flat as T$\to $0, and so can be fit to a single-gap BCS model. In contrast, the lower purity sample showed an increase in the zero-field $\mu$SR relaxation rate below T$_c$ corresponding to a characteristic field strength of 0.6 G. While the temperature-dependence of the superfluid density was also found to be consistent with a single-gap BCS model, the magnitude as T$\to $0 was found to be much lower for a given applied field than in the case of the high purity sample. These findings suggest that the dominant pairing symmetry in high quality Mg$_{10}$Ir$_{19}$B$_{16}$ samples corresponds to the spin-singlet channel, while sample quality drastically affects the superconducting properties of this system.