High Resolution Polar Kerr Effect Measurements of Sr2RuO4: Evidence for   Broken Time Reversal Symmetry in the Superconducting State
  Polar Kerr effect in the spin-triplet superconductor Sr2RuO4 was measured with high precision using a Sagnac interferometer with a zero-area Sagnac loop. We observed non-zero Kerr rotations as big as 65 nanorad appearing below Tc in large domains. Our results imply a broken time reversal symmetry state in the superconducting state of Sr2RuO4, similar to He3-A. 
Jing Xia, Maeno Yoshiteru, Peter T. Beyersdorf, M. M. Fejer, Aharon   Kapitulnik