Session 23V

Recent Trends in Heavy-Fermion Physics

Frank Steglich

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

We discuss UPd₂Al₃, YbRh₂Si₂ and U₂Ru₂Sn to illustrate recent developments in heavy-fermion physics. UPd₂Al₃ is the first unconventional superconductor for which tunneling and inelastic neutron-scattering results highlight a non-phononic, i.e., magnetic-exciton mediated, pair state. YbRh₂Si₂ represents a model system exhibiting a magnetic quantum critical point at which both the effective quasiparticle-quasiparticle scattering cross section and the effective quasiparticle mass appear to diverge. The strongly correlated semimetal U₂Ru₂Sn shows similarities to the prototypical Kondo insulator CeNiSn, albeit with a ten times larger pseudogap.
Work done in collaboration with: M. Baenitz, J. Custers, P. de V. du Plessis, P. Gegenwart, C. Geibel, S. Mederle, K. Neumaier, S. Paschen, N. Sato, G. Sparn, A.M. Strydom, H.V. Tran and H. Wilhelm.

Superconductivity in MgB₂ and its related new Boron compounds

Jun Akimitsu

Department of Physics, Aoyama-Gakuin University, 6-16-1 Chitsedai, Setagaya-ku, Tokyo 157-8572, Japan

In 2000, we reported the superconductivity at 39 K in MgB₂, of which transiton temperature is highet among the metal superconductor. In this conferrence, we review the present experimental situation of this material. We also discuss the new superconductors including borons with low-T_c discovered in my laboratory.