Dresden 2006 – wissenschaftliches Programm
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MA: Magnetismus
MA 22: Internal Symposium “50 Years AG Magnetism”
MA 22.5: Hauptvortrag
Mittwoch, 29. März 2006, 17:30–18:00, HSZ 03
Interplay between Incipient Magnetism and Superconductivity in Heavy Fermions — •Frank Steglich — Max Planck Institute for Chemical Physics of Solids, 01187 Dresden, Germany
Strong electronic correlations on partially filled 4f or 5f shells, weakly hybridized with ligand valence-electron orbitals, cause the formation of extremely heavy quasiparticles composed of a dominating local f part as well as contributions from conduction-band states. As discovered in 1979 for CeCu2Si2, these “heavy fermions” (HF) may form Cooper pairs. In most HF metals, the superconducting glue seems to be of magnetic origin. In fact, for UPd2Al3 magnetic-exciton mediated pairing could be convincingly demonstrated, i.e. by comparing quasiparticle-tunneling and inelastic neutron-scattering results.
For a number of Ce-based HF metals superconductivity was found to be intimately related to the existence of an antiferromagnetic (AF) instability which, at least in the case of CeCu2Si2, is of the conventional (spin-density-wave) type. On the other hand, an AF magnetic-field induced “quantum critical point” of unconventional nature originating in a break up of the “composite” HFs was recently established in YbRh2Si2. For this compound, we found dominating 2D ferromagnetic quantum critical fluctuations in wide regions of the phase diagram, but no superconductivity at temperatures down to 10 mK.
Work done in collaboration with: M. Deppe, G. Donath, J. Ferstl, P. Gegenwart, C. Geibel, H.S. Jeevan, R. Küchler, T. Lühmann, M. Nicklas, N. Oeschler, J. Sichelschmidt, O. Stockert, P. Thalmeier, F. Weickert, S. Wirth.