Eur. Phys. J. B 27, 29-48 (2002)
https://doi.org/10.1140/epjb/e20020127

Dual model for magnetic excitations and superconductivity in UPd₂Al₃

Max-Planck-Institute for Chemical Physics of Solids, 01187 Dresden, Germany

Corresponding author: ^a thalm@cpfs.mpg.de

Received: 22 October 2001
Revised: 28 February 2002
Published online: 15 May 2002

Abstract

The Heavy Fermion state in UPd₂Al₃ may be approximately described by a dual model where two of the three U-5f electrons are in a localized state split by the crystalline electric field into two low lying singlets with a splitting energy  meV. The third 5f electron has itinerant character and forms the Heavy Electron bands. Inelastic neutron scattering and tunneling experiments suggest that magnetic excitons, the collective propagating crystal field excitations of the localized 5f electrons, mediate superconducting (sc) pairing in UPd₂Al₃. A theory for this novel mechanism is developed within a nonretarded approach. A model for the magnetic exciton bands is analyzed and compared with experiment. The sc pair potential which they mediate is derived and the gap equations are solved. It is shown that this mechanism favors an odd parity state which is nondegenerate due to the combined symmetry breaking by the crystalline electric field and the AF order parameter. A hybrid model including the spin fluctuation contribution to the pairing is also discussed.