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Project leader: M. Sigrist (ETHZ)
Participating members: D. Baeriswyl (UniFR), G. Blatter (ETHZ), L. Degiorgi (ETHZ), Ø. Fischer (UniGE), E. Giannini (UniGE), D. Jaccard (UniGE), M. Kenzelmann (PSI), E. Morenzoni (PSI), H.-R. Ott (ETHZ), T. M. Rice (ETHZ), M. Sigrist (ETHZ), M. Troyer (ETHZ), D. van der Marel (UniGE).

Summary

Today, a wide class of materials exhibiting special properties due to the presence of strong local correlation between the position and the motion of electrons is known. The present project will complement the study of the transition metal oxides in Project 4 with work on heavy fermion materials, featuring electrons in partially filled localized 4f-shells weakly hybridized with the conduction bands. A special property of these materials is the presence of closely competing electronic groundstates, with the quantum phase transitions occurring between them as external parameters are varied. Superconductivity appearing in the vicinity of a magnetic quantum phase transition or a valence crossover is an example of special interest. These phenomena occur, for instance, in various Ce-based superconductors, such as the Ce-115 series, the non-centrosymmetric superconductors such as CePt₃Si, CeRhSi₃, and CeCoGe₃ and CeCu₂Si₂. The investigation of these unconventional superconductors has to address a range of issues, such as the anomalous high-field low-temperature properties of the mixed superconducting phase, the consequences for the vortex matter induced by high magnetic fields, and the appearance of unusual quasiparticle spectra, in particular near surfaces and interfaces. Several of the heavy fermion compounds, and more generally 4f-electron systems, will be investigated for their diverse and intriguing magnetic properties, with the aim to elucidate the role of the nearly localized f-electrons under various circumstances. The project will also include the study of magnetic and optical properties of non-centrosymmetric transition metal silicides and related materials, with the goal of addressing the effects of correlation, band structure, quantum fluctuations, and spin-orbit coupling. Emphasis will be given to a wide range of spectroscopic studies which profit from the unique combination of techniques available within MaNEP. On the theoretical side, collaborative efforts with experimental studies will be accompanied by the development of new analytic and computational techniques which can be used to analyze various correlated electron systems and their intriguing electronic phases.