The aim of the Workshop Hidden Order, Superconductivity and Magnetism in URu2Si2 was to understand strongly correlated electron materials by focusing on the metallic heavy fermion (HF) systems. Among the many intermetallic HF compounds one particular material stands out, viz., URu2Si2 whose above-titled behavior has puzzled researchers for 30 years. By bringing ca. 45 experts, i.e., active researchers in the HO problem, together for 5 intense days (plus some of the 2 weekends) of discussions and debates, progress and understanding were accomplished by:                                                                                                               

i)              Creating relationships and correlations among the different experimental techniques, e.g., ARPES and quantum oscillations, and STM/STS and optical spectroscopy.

ii)             Use of density functional theory as a guiding principle for experimental comparisons.

iii)            Searching out the valid theoretical description of certain experiments.

iv)           Identifying  areas of ambiguous or controversial experimental results.

v)            Eliminating theories or models through their invalid experimental predictions.

vi)           Deriving consensus towards a valid description of HO and its coexisting superconductivity and nearby magnetism.

vii)          Listing future steps for a complete and final understanding of the HO problem which unfortunately was not reached during the workshop.

A unique form of the lecture sessions was to have 2 experimentalists present their latest results on a particular technique with full audience discussions, then after a coffee/tea break a theorist, whose work is directly related to the specific experiment, offers a criticism and a comparison. Naturally there is ongoing scrutiny from the participants which often needs to be controlled by a strict session moderator. The dialogue usually continues into the 2 hour lunch break or evening venue. We found that this “trimer” experiment/theory session functioned quite well and led to an enhanced stimulation of questions and interactions. And we recommend its future use in other workshops where there exists a need for comparison between experiment (data) and theory (models). So with the impulse of the trimer sessions we generated a continuing and penetrating debate throughout the workshop.  Posters were viewable the entire week and generated additional areas of discussion.

The workshop began with 2 general overview talks on HF and HO. Wednesday afternoon was devoted to the very latest experiments, polar Kerr effect and Raman scattering, followed by 2 explanations of the state of the theory. There were 7 of the above-described trimer sessions. And at the concluding session 2 senior theorists and 2 of the organizers give their views and thoughts on the workshop. These and the reactions from the participants were very positive and indicated a most successful and stimulating event. After the return of some participants a series of “thank you” notes were received in Leiden to confirm the above. In addition a number of manuscripts of new results that were generated by the workshop have been submitted to leading scientific journals.

Financial support for the workshop was garnered from Royal Netherlands Academy of Arts and Sciences (KNAW), National Science Foundation (NSF) and Institute for Complex Adapted Matter (ICAM), Institute Lorentz (IL) and Lorentz Center (LC). This funding included lodging, lunch and travel support for the needy, mostly USA, participants. We are most grateful for this generous support which not only enhanced the workshop venue but further stimulated its scientific component.

And most important was the competent advice, assistant and coordination of the Lorentz Center with its highly competent staff and organizational ability. This daily support allowed the workshop to become a focused scientific event and not a bureaucratic episode. We extend our heartfelt appreciations and thanks to the staff of the LC for making the workshop a singular scientific happening.

The Organizers
Yuji Matsuda, John Mydosh, Peter Oppeneer, and Jan Zaanen

28 December 2013