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

报告人简介：
Prof. Frank Steglich is a world leading scientist in unconventional superconductivity and quantum criticality. Among his major scientific achievements is the discovery of the superconductivity in Heavy Fermions in 1979. He became a full professor in Darmstadt Univ. of Technology in 1980. He is the founding director of the Max Planck Institute for Chemical Physics of Solids (since 1996), and the Vice President of the DFG of Germany (2001-2007).

Prof. Steglich received numerous awards and prizes, including Academy Stipend of the Volkswagen Foundation (1986), Gottfried Wilhelm Leibniz Prize (DFG) (1986), Hewlett Packard Europhysics Prize (1989), Alexander von Humboldt Award for the Promotion of the Scientific Cooperation between France and the Federal Republic of Germany (1989), American Physical Society International Prize for New Materials (1990), International Union of Pure and Applied Physics (IUPAP) Magnetism Award (2000), Leibniz Medal of the IFW Dresden (2001), Stern Gerlach Medal of the German Physical Society (DPG) (2004), Order of Merit (Gro？es Bundesverdienstkreuz) of the Federal Republic of Germany (2005) and Bernd T. Matthias Prize for Superconducting Materials (2006). He also received honorary doctorate and professorship from many institutions and universities worldwide. He served as the editor-in-chief of Zeitschrift fur Physik B for many years.

报告摘要：In this talk, the extent to which incipient antiferromagnetic (AF) order may assist heavy-fermion superconductivity (SC) is discussed. I will present recent results on the prototypical heavy-fermion superconductor CeCu2Si2 and the isostructural compound YbRh2Si2.
The former material shows an AF quantum critical point of the conventional spin-density wave (SDW) type, whereas for the latter one, the AF instability appears to coincide with a break down of the Kondo effect [1]. This unique behavior is illustrated by Hall-effect [2] and thermopower [3] data. It is also held responsible for the unusual critical scaling, found in the specific-heat results when approaching the classical AF phase transition at TN=70mK [4]. I will show in addition, how the AF and the Kondo-break-down quantum-critical points are detached when chemical pressure is applied to YbRh2Si2 [5].
New inelastic neutron scattering results on CeCu2Si2 highlight Cooper pairing mediated by SDW fluctuations [6]. On the other hand, no SC could yet be observed for high-quality single crystals of YbRh2Si2 down to T≈10mK [1]. The (non-) existence of SC near a Kondo-break-down instability remains to be an intriguing topic for future investigations.

1. Q. Si and F. Steglich, Science 319, 1161 (2010).
2. S. Friedemann et al., PNAS 107, 14547 (2010).
3. S. Hartmann et al., Phys. Rev. Lett. 104, 09401 (2010).
4. C. Krellner et al., Phys. Rev. Lett. 102, 196402 (2009).
5. S. Friedemann et al., Nature Phys. 5, 465 (2009).
6. O. Stockert et al., Nature Phys. 7, 119 (2011).

联系人：金奎娟 研究员（82648099）
报告邀请人：王楠林 研究员  (82649584)