Scientific report

Third International Workshop on the Dual Nature of f-Electrons

Workshops on the Dual Nature of f-electrons are organized by the same group biannually since 2006. The first event was organized in Santa Fe, NM, USA in 2006, next in 2008 at same location. This year we moved to Dresden in order to attract the broader spectrum of european scientists. The number of speakers went up from 18 in 2006 and 17 in 2008 to 36 in the current edition. This number proves that Dresden was an excellent choice, with a guaranteed broad participation of scientists involved in f-electron research.The conference is traditionally focused on the issues of f-electron materials.

Just to list a few participants, we note the talk by Zachary Fisk on quantum criticality, a "blackboard presentation" by Gertrud Zwicknagl on the dual life of f-electrons and Gerry Lander's on neutron scattering in f-electron research. We also had a priviledge to listen to Peter Riseborough, John Mydosh, Peter Oppeneer, Ladia Havela and Gabi Kotliar and several other excellent presentations. Dominant topics were: electronic structure and properties, superconductivity and magnetism, new materials, Kondo physics, competing ground states and quantum criticality. It is a tradition of the workshop to have a more or less even mix of theory and experiment, and to devote two afternoons to topical sessions and discussion panels. Students and postdocs presented three talks and several posters, and their presentation style and the message were very well accepted by the participants.

For this meeting, we decided to choose two specific areas for topical sessions and discussion panels: URu₂Si₂ and DMFT. The enigmatic hidden order state in URu₂Si₂ generates lot of interest in the community, with several novel results in both theory and experiment presented during the last two years. The six topical talks and a discussion panel were very well attended, and the discussion can be counted as one of the most heated debates in the field.

From the scientific point of view, out of over 30 or so theories attempting to describe the hidden order phase, two seem to be surfacing. One theory approaches the order parameter question frokm the point of view of the fluctuation induced lattice symmetry breaking, leading to well developed and strongly k-dependent gapping of the Fermi surface. In this approach, time-reversal symmetry is broken on a timescale comparable to the fluctuations time. The other, DMFT-based approach, describes the formation of multipolar order in the HO phase, which by itself does not invoke time-reversal symmetry breaking. As a result of this discussion it became clear that a careful new experiment confirming or excluding time-reversal symmetry breaking would help confirm one of the models.

The second panel of four talks and discussion session was devoted to the aspects of Dynamical Mean Field Theory (DMFT). The discussion showed that several approaches to DMFT from different groups are not always parallel, and important details like for example the treatment of RKKY interaction, require further clarification. Neverheless, DMFT remains the rapidly growing approach to calculating many-body effects in f-electron systems. It has to be noted that the scientific coordinators are univocal in admiration for impeccable organization of the event provided by MPI-PKS. The institute is considerably helping the physics community. Mrs. Lantsch who was in charge for the workshop did an admirable job.

We would like to build on this success and we are contemplating the possibility of organizing the focused f-electron photoemission workshop in Dresden. There is a lot of new information coming up in ARPES and in calculations, and the field is evolving rapidly. It would be excellent to capture this energy and have most of the players in the field meet in one place for an exciting exchange of information. We can not think of a better place than MPI-Dresden to have this event, perhaps in the early Fall of 2012.

P. Fulde, G. Zwicknagl, T. Durakiewicz
June 2nd 2010

For further information please e-mail to: dual10@pks.mpg.de