Important Notice
1) Shuttle from LIG Ingenium to SKKU
May 28th, 2014
At 1:00pm and 5:30pm

2) Shuttle from SKKU to LIG Ingenium
May 28th, 2014
At 8:30pm (after welcome reception)

3) Welcome Reception at Biz Cafe, 1st floor of Corporate Collaboration Center, SKKU
At 6:30pm

4) Tutorial at SKKU at 2:00pm on May 28th, 7th Floor of Samsung Library

The Fifth International Workshop on the Dual Nature of f-Electrons

May 28 (Wed) - 31 (Sat), 2014, Suwon, Korea
Scope of the Workshop

This workshop is aimed to provide an avenue to discuss discoveries and progress on the dual nature of f-electrons in multitude of systems. Topics that will be covered in this workshop include, but are not limited to (i) understanding the physical properties of correlated systems and heavy fermions, (ii) unraveling the physical principles of f-electron materials with special emphasis on Ce, U and Pu compounds, and (iii) new materials that show a correlated electronic behavior.

History of the Workshop

Period Area
1st workshop Jul. 16 - Jul. 18, 2006 Santa Fe, USA
2nd workshop Jun. 28 - Jul. 1, 2008 Santa Fe, USA
3rd workshop May 25 -May 28, 2010 Dresden, Germany
4th workshop July 4 - July 6, 2012 Himeji city, Japan

Motivation of the Workshop

   When atoms form a solid, the fate of their outer-shell electrons is determined qualitatively by a tradeoff between kinetic and potential energies that leads to the formation of dispersive bands. This simple picture, combined with Pauli's exclusion principle, forms the basis for understanding why solids are metallic, semiconducting or insulating and why solids crystallize in particular structures. Electrons also interact with each other and with their chemical environment. These interactions give rise to phase transitions, such as crystallographic changes, magnetic order, and conventional superconductivity. By the early 1980's, substantial success of these concepts invoked claims that the physics of solids was rapidly becoming a solved problem. At that time, there were, however, a few 'anomalous' solids; some were insulators or non-magnetic when they should have been metals or magnetic. We now understand that these 'anomalies' are the rule for classes of materials. They arise from very strong repulsive Coulomb and spin-orbit interactions that must be treated on an equal footing with kinetic and potential energies. The physics of these anomalous d-and f-electron materials is exceptionally non-trivial. The Coulomb and spin-orbit interactions create a complex and highly correlated electronic state whose response is controlled collectively by all of the outer-shell electrons. This complexity generates a rich spectrum of physical states and exotic behaviors that pose the grandest challenging questions for today's condensed matter physics.

   Minimal models that include strong electron-electron interactions are crucial to describe the physics of transition metals (3d systems) and lanthanide (4f systems) compounds. A multi-orbital Hubbard-like model captures the basic physics of 3d systems. Recent solutions of the Periodic Anderson Model (PAM) confirm that it contains at least part of the essential physics of 4f systems. The solutions of these models thus account for gross consequences of electronic correlations, i.e., the aforementioned 'anomalous' behaviors in 3d and 4f systems. The modeling for the 4f materials, however, appears incomplete and, for the 5f systems (actinides), inadequate. In neither model, do outer-shell electrons assume the dual roles of being simultaneously localized and itinerant (band-like). Nevertheless, a set of experiments on correlated 4f- and 5f-electron materials during the past four years argues precisely for this seemingly contradictory duality. Particularly compelling experiments (e.g., Phys. Rev. Lett. 92, 016401 (2004)) on cerium compounds show that the single 4f-electron of cerium is localized at room temperature and partially 'dissolves' with decreasing temperature into a highly correlated band state but retains some fraction of its localized nature. Similarly, low-temperature experiments on correlated uranium compounds (e.g. Nature 410, 340 (2001)) find that electrons in uranium's 5f-orbital simultaneously participate in magnetic ordering of localized electrons and in forming a correlated band of itinerant electrons out of which unconventional superconductivity emerges. These experiments imply that duality imposed by strong correlations drives states in which low energy spin and charge degrees of freedom cannot be disentangled. The Fermi surface of these unconventional metals will reflect these unusual properties and may also be composed of more than one component. Such duality could provide a natural explanation for the homogeneous coexistence of multiple broken symmetries, e.g., magnetism and superconductivity, found in some cerium and uranium compounds, for the reconciliation of experimental observations with theories of quantum criticality, and for the unexplained relationships between photoemission spectra and ordered magnetic moments.

   Plutonium is particularly germane. The ad hoc assumption that its 5f electrons are simultaneously localized and itinerant gives the correct equilibrium volume for d-Pu, but why this assumption seems to be correct and why the localized fraction of 5f electrons should pair in a special configuration are not understood.

   Recent theoretical effort is available, where the dual nature of f electrons is applied in explaining the ground state properties for Pu metal and a limited number of heavy fermion superconductors. We also have some initial indications from experiment allowing the explanation of the electronic structure features by assuming duality of the f electrons. It seems necessary, at this initial stage of development, to confront both sides: theory and experiment, and attempt to discuss both the present level of understanding and - more importantly - the directions to be explored in the future.
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