Quantum phase diagram of antiferromagnetism and superconductivity with a tetracritical point in CeRhIn5 in zero magnetic field

We report on a pressure-temperature phase diagram of antiferromagnetism (AFM) and superconductivity (SC) in CeRhIn5 studied by the nuclear-quadrupole-resonance measurements under pressure. It is demonstrated that an AFM phase transition takes place inside the superconducting state. This result reveals that a tetracritical point exists in the phase diagram of AFM and SC at zero magnetic field. The finding of unconventional SC characteristics in the uniformly coexisting phase of AFM and SC suggests that both phases may be mediated by the same magnetic interaction.