Coexistence of antiferromagnetism and superconductivity in heavy-fermion systems

We report the novel pressure (P)-temperature (T) phase diagrams of antiferromagnetism (AFM) and superconductivity (SC) in CeRhIn 5 , CeIn 3 , and CeCu 2 Si 2 revealed by the nuclear quadrupole resonance measurement. In the itinerant helical magnet CeRhIn 5 , we found that the Neel temperature T N is reduced at P ≥ 1.23 GPa with an emergent pseudogap behavior. The coexistence of AFM and SC is found in a narrow P range of 1.63-1.75 GPa, followed by the onset of SC with line-node gap over a wide P window 2.1-5 GPa. In CeIn 3 , the localized magnetic character is robust against the application of pressure up to P 1.9 GPa, beyond which the system evolves into an itinerant regime in which the resistive superconducting phase emerges. We discuss the relationship between the phase diagram and the magnetic fluctuations. In CeCu 2 Si 2 , the SC and AFM coexist on a microscopic level once its lattice parameter is expanded. We remark that the underlying marginal AFM state is due to collective magnetic excitations in the superconducting state in CeCu 2 Si 2 . An interplay between AFM and SC is discussed on the SO(5) scenario that unifies AFM and SC. We suggest that the SC and AFM in CeCu 2 Si 2 have a common mechanism.