Extremely High Upper Critical Magnetic Field of the Noncentrosymmetric Heavy Fermion SuperconductorCeRhSi3

Abstract

We report an extremely high upper critical field $B_{c2}$ in the noncentrosymmetric heavy fermion superconductor ${\mathrm{CeRhSi}}_3$ for a magnetic field $B$ along the tetragonal $c$ axis. $B_{c2}(T=0)$ possibly reaching 30 T is much higher than $B_{c2}(0)=7\mathrm{T}$ for $B\perp c$ and greatly exceeds the paramagnetic limiting field. The strong anisotropy of $B_{c2}(0)$ with extremely high $B_{c2}(0)$ for $B\parallel c$ is qualitatively explained by the paramagnetic pair-breaking mechanism specific to the noncentrosymmetric superconductor. However, an unusual $B_{c2}(T)$ curve with a positive curvature for $B\parallel c$ cannot be explained satisfactorily by conventional orbital pair-breaking models.