Muon spin rotation/relaxation measurements of the noncentrosymmetric superconductor Mg₁₀ Ir₁₉B₁₆

We have searched for time-reversal symmetry-breaking fields in the noncentrosymmetric superconductor Mg10 Ir19 B16 via muon spin relaxation (μSR) in zero applied field. We also 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 significantly 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→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 μSR relaxation rate below Tc 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→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 Mg10 Ir19 B16 is a superconductor characterized by a single-gap function with no nodes and sample quality drastically affects the superconducting properties of this system.