title: Hidden magnetism and quantum criticality in the heavy fermion superconductor CeRhIn5.
abstract: With only a few exceptions that are well understood, conventional superconductivity does not coexist with long-range magnetic order (for example, ref. 1). Unconventional superconductivity, on the other hand, develops near a phase boundary separating magnetically ordered and magnetically disordered phases. A maximum in the superconducting transition temperature T(c) develops where this boundary extrapolates to zero Kelvin, suggesting that fluctuations associated with this magnetic quantum-critical point are essential for unconventional superconductivity. Invariably, though, unconventional superconductivity masks the magnetic phase boundary when T < T(c), preventing proof of a magnetic quantum-critical point. Here we report specific-heat measurements of the pressure-tuned unconventional superconductor CeRhIn5 in which we find a line of quantum-phase transitions induced inside the superconducting state by an applied magnetic field. This quantum-critical line separates a phase of coexisting antiferromagnetism and superconductivity from a purely unconventional superconducting phase, and terminates at a quantum tetracritical point where the magnetic field completely suppresses superconductivity. The T --> 0 K magnetic field-pressure phase diagram of CeRhIn5 is well described with a theoretical model developed to explain field-induced magnetism in the high-T(c) copper oxides, but in which a clear delineation of quantum-phase boundaries has not been possible. These experiments establish a common relationship among hidden magnetism, quantum criticality and unconventional superconductivity in copper oxides and heavy-electron systems such as CeRhIn5.
authors.affiliation: Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA. tuson@lanl.gov
authors.forename: Tuson
authors.initials: T
authors.lastname: Park
authors.forename: F
authors.initials: F
authors.lastname: Ronning
authors.forename: H Q
authors.initials: HQ
authors.lastname: Yuan
authors.forename: M B
authors.initials: MB
authors.lastname: Salamon
authors.forename: R
authors.initials: R
authors.lastname: Movshovich
authors.forename: J L
authors.initials: JL
authors.lastname: Sarrao
authors.forename: J D
authors.initials: JD
authors.lastname: Thompson