Bereiche | Tage | Auswahl | Suche | Downloads | Hilfe

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.