New quantum phase in the heavy fermion superconductor CeRhIn5

Pressure dependence on the specific heat of CeRhIn5 has been studied for magnetic field perpendicular to the ab-plane. Similar to the field parallel to the ab-plane [T. Park et al., Nature 440 (2006) 65], magnetic field reveals hidden magnetism in the mixed superconducting state above 1.75 GPa where antiferromagnetism disappears at zero field. The specific heat anomaly at Tc is initially suppressed with increasing field, but becomes enhanced with further increasing field, indicating that the nature of the superconducting (SC) transition may have changed from second to first order. Together with the coexisting phase of the field-induced magnetism and superconductivity, the first-order like SC transition in CeRhIn5 may provide insight to the inhomogeneous SC state (or FFLO state) observed in CeCoIn5.