title: Superconducting pairs with extreme uniaxial anisotropy in URu2Si2.
abstract: We report magnetic field orientation-dependent measurements of the superconducting upper critical field in high quality single crystals of URu(2)Si(2) and find the effective g factor estimated from the Pauli limit to agree remarkably well with that found in quantum oscillation experiments, both quantitatively and in the extreme anisotropy (≈10(3)) of the spin susceptibility. Rather than a strictly itinerant or purely local f-electron picture being applicable, the latter suggests the quasiparticles subject to pairing in URu(2)Si(2) to be "composite heavy fermions" formed from bound states between conduction electrons and local moments with a protected Ising behavior. Non-Kramers doublet local magnetic degrees of freedom suggested by the extreme anisotropy favor a local pairing mechanism.
authors.affiliation: Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA.
authors.forename: M M
authors.initials: MM
authors.lastname: Altarawneh
authors.forename: N
authors.initials: N
authors.lastname: Harrison
authors.forename: G
authors.initials: G
authors.lastname: Li
authors.forename: L
authors.initials: L
authors.lastname: Balicas
authors.forename: P H
authors.initials: PH
authors.lastname: Tobash
authors.forename: F
authors.initials: F
authors.lastname: Ronning
authors.forename: E D
authors.initials: ED
authors.lastname: Bauer