Polar Kerr Effect from Time-Reversal Symmetry Breaking in the Heavy-Fermion Superconductor PrOs_{4}Sb_{12}.

We present polar Kerr effect measurements of the filled skutterudite superconductor PrOs_{4}Sb_{12}. Simultaneous ac susceptibility measurements allow us to observe the superconducting transition under the influence of heating from the optical beam. A nonzero Kerr angle θ_{K} develops below the superconducting transition, saturating at ∼300 nrad at low temperatures. This result is repeated across several measurements of multiple samples. By extrapolating the measured θ_{K}(T) to zero optical power, we are able to show that the Kerr angle onset temperature in one set of measurements is consistent with the transition to the B phase at T_{C2}. We discuss the possible explanations for this result and its impact on the understanding of multiphase and inhomogeneous superconductivity in PrOs_{4}Sb_{12}.