Competitive coexistence of superconductivity with antiferromagnetism in CeRhIn5

We carried out ac magnetic susceptibility measurements under pressures P on the heavy fermion antiferromagnet CeRhIn5. We report bulk superconductivity (SC) at ambient pressure with a transition temperature T-c similar or equal to 90 mK. The degraded SC in a powdered or polished sample was restored by annealing, showing that the SC state is sensitive to inhomogeneity. In a coexistence region of the SC with antiferromagnetism (AF), we find that T-c(P)T-n(N)(P)(1-n)=const where T-N indicates a Neel temperature and n denotes a ratio of electronic specific heat coefficients below and above T-N, indicating the competition of the SC and the AF for states at the Fermi surface.