Coexistence of antiferromagnetism and superconductivity in heavy-fermion systems

Abstract

We report the novel pressure ( P)–temperature ( T) phase diagrams of antiferromagnetism (AFM) and superconductivity (SC) in CeRhIn 5, CeIn 3, and CeCu 2Si 2 revealed by the nuclear quadrupole resonance measurement. In the itinerant helical magnet CeRhIn 5, we found that the Néel 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 2Si 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 2Si 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 2Si 2 have a common mechanism.