title: Observation of two distinct superconducting phases in CeCu2Si2.
abstract: We report the presence of two disconnected superconducting domes in the pressure-temperature phase diagram of partially germanium-substituted CeCu2Si2. The lower density superconducting dome lies on the threshold of antiferromagnetic order, indicating magnetically mediated pairing, whereas the higher density superconducting regime straddles a weakly first-order volume collapse, suggesting a pairing interaction based on spatially extended density fluctuations. Two distinct pairing mechanisms thus appear to operate in the single, wide, superconducting range of stoichiometric CeCu2Si2, both of which might apply more generally to other classes of correlated electron systems.
authors.affiliation: Max-Planck-Institute for Chemical Physics of Solids, Nöthnitzer Strabetae 40, 01187 Dresden, Germany. yuan@cpfs.mpg.de
authors.forename: H Q
authors.initials: HQ
authors.lastname: Yuan
authors.forename: F M
authors.initials: FM
authors.lastname: Grosche
authors.forename: M
authors.initials: M
authors.lastname: Deppe
authors.forename: C
authors.initials: C
authors.lastname: Geibel
authors.forename: G
authors.initials: G
authors.lastname: Sparn
authors.forename: F
authors.initials: F
authors.lastname: Steglich