Extremely high upper critical magnetic field of the noncentrosymmetric heavy fermion superconductor CeRhSi3

We report an extremely high upper critical field Bc2 in the noncentrosymmetric heavy fermion superconductor CeRhSi3 for a magnetic field B along the tetragonal c axis. Bc2(T=0) possibly reaching 30 T is much higher than Bc2(0)=7T for B c and greatly exceeds the paramagnetic limiting field. The strong anisotropy of Bc2(0) with extremely high Bc2(0) for Bc is qualitatively explained by the paramagnetic pair-breaking mechanism specific to the noncentrosymmetric superconductor. However, an unusual Bc2(T) curve with a positive curvature for Bc cannot be explained satisfactorily by conventional orbital pair-breaking models.