Virtual proceedings of Hvar 2005 conference and workshop on correlated systems

This proceedings presents lectures and posters given at the third in a series of workshops and conferences on the topic of electron correlation we have held on the island of Hvar. The first two in 1999 and 2002, and the current one in 2005. The workshop took place from September 25th  to 30th and the conference from September 30th to October 5th. The aim of these meetings has been to bring together some of the most active experimental and theoretical physicists working in the field to review the current issues in the physics of strong electron correlation. The virtual proceedings should facilitate the dissemination of scientific achievement reported at the workshop and the conference.

Conference on Concepts in Electron Correlation

We are still living through exciting times. The central topics of the original conference, the diverse and puzzling electronic properties of heavy fermions,  high temperature superconductors, and transition metal oxides  still present formidable challenges. However, we are getting more and more specific information from the hard work of the experimental community. The aim of the meeting was not so much to offer the 'present day solution' of various anomalies observed in strongly correlated systems but, rather, to characterize and describe the anomalies, so as to find a common element in the experimental results.

The resolution possible in photoemission experiments has increased by an order of magnitude giving us much more detailed information on the excitations in the high temperature cuprate superconductors, for instance. We are also now beginning to learn more about the effects of phonon coupling--- a topic which is deservedly  attracting more attention.

Thanks also to the efforts  of a section of  theoretical community there has been real effort to describe  specific compounds through a combination of local density theory and dynamical mean field theory. This work may be entering a new phase in which theoretical predictions may point the way to new experiments. The fundamental work in trying to understand the quantum critical point in heavy fermion materials, and the non-Fermi liquid behaviour when magnetic order is suppressed, is moving in new directions, and it will be interesting to observe how this work develops.

One of the major changes since the first conference has been the  remarkable advances in nanotechnology which have added new classes of strongly correlated systems, purpose-designed materials, such a quantum dots and carbon nanotubes. These systems have a fascination both for experimentalists and theoreticians.  For the experimentalists they offer the potential for exploring new effects in  novel situations. Besides the stimulus to theoretical work, they also  offer much more scope for testing theory. The parameters  can be changed via gate voltages in a controlled way, and different  regimes can be explored in a ways often not possible with the more conventional materials.

Even more remarkable is some of the work on cold atomic gases where even the interactions between the atoms can be modified through a magnetic field due to the Feshbach resonance. So the crossover from strong repulsion to strong attraction can be explored.

Another whole area of activity which has been stimulated by  nanoscale materials is non-equilibrium phenomena. Most of the non-perturbative techniques which have been the devised  tackling strong correlation models, such as the renormalization group or Bethe ansatz approaches, cannot be straightforwardly generalised to non-equilibrium situations, and so considerable effort is being made to devise strategies for overcoming these difficulties.   These issues and developments were all touched upon in the contributions to the 2005 conference. Most of them have been made available to read and  download from this web page.

Workshop on Correlated Thermoelectrics

Recent achievements in condensed matter physics and chemistry have brought us to the point where the material properties can be tuned on the quantum mechanical level. We are interested in the possibility of engineering the thermoelectric devices for low-temperature applications using the correlated electron systems close to the metal-insulator boundary. The thermoelectric workshop focused on Kondo insulators, correlated semiconductors, skutterudites, and related heterostructures, and reviewed new materials and mechanisms that could lead to thermoelectric devices with a useful figure-of-merit below 77 K.

Our goal in then field of correlated thermoelectrics is to acquire the knowledge required to achieve control over the relevant degrees of freedom and to engineer new thermoelectric materials with specific quantum mechanical properties. From the complexity of the problem it is clear that engineering of such devices cannot be successful without input from the fundamental research. One has to solve the chemical and metallurgical problems to produce new materials, one needs accurate characterization of the physical properties of these highly complex chemical structures in order to understand the systematic trends, and one has to perform theoretical modeling of various quantum mechanical effects in strongly correlated systems.

It is important for progress in this field to have a stimulating dialogue between chemists, metallurgists and physicists. The success is only likely to be achieved through a combination of techniques in a multi-front approach and the aim of the workshop was  to provide the opportunity to step back and look at the bigger picture.

V. ZlatiŠ, Institute of Physics, Zagreb
A. Hewson, Imperial College, London
J. Freericks, Georgetown Unversity, Washington D.C.