Time-Reversal Symmetry Breaking Superconductivity in Sr2RuO4
  We report muon spin relaxation measurements on the superconductor Sr2RuO4 that reveal the spontaneous appearance of an internal magnetic field below the transition temperature: the appearance of such a field indicates that the superconducting state in this material is characterized by the breaking of time-reversal symmetry. These results, combined with other symmetry considerations, suggest that superconductivity in Sr2RuO4 is of p-wave (odd-parity) type, analogous to superfluid 3He. 
G.M.Luke, Y.Fudamoto, K.M.Kojima, M.I.Larkin, J.Merrin, B.Nachumi,   Y.J.Uemura, Y.Maeno, Z.Q.Mao, Y.Mori, H.Nakamura and M....