Evidence for Time-Reversal-Symmetry-Broken Superconductivity in Locally   Noncentrosymmetric SrPtAs
  We report the magnetic and superconducting properties of locally noncentrosymmetric SrPtAs obtained by muon-spin-rotation/relaxation (muSR) measurements. Zero-field muSR reveals the occurrence of small spontaneous static magnetic fields with the onset of superconductivity. This finding suggests that the superconducting state of SrPtAs breaks time-reversal symmetry. The superfluid density as determined by transverse field muSR is nearly flat approaching T = 0 K proving the absence of extended nodes in the gap function. By symmetry, several superconducting states supporting time-reversal symmetry breaking in SrPtAs are allowed. Out of these, a dominantly d + id (chiral d-wave) order parameter is most consistent with our experimental data. 
P. K. Biswas, H. Luetkens, T. Neupert, T. Stuerzer, C. Baines, G.   Pascua, A. P. Schnyder, M. H. Fischer, J. Goryo, M. R. L...
cond-mat.supr-con cond-mat.str-el