Thermoelectric devices could play an important role in making efficient use of our energy resources but their efficiency would need to be increased for their wide scale application. There is a multidisciplinary search for materials with an enhanced thermoelectric responses for use in such devices. This volume covers the latest ideas and developments in this research field, covering topics ranging from the fabrication and characterization of new materials, particularly those with strong electron correlation, use of nanostructured, layered materials and composites, through to theoretical work to gain a deeper understanding of thermoelectric behavior. It should be a useful guide and stimulus to all working in this very topical field.

The NATO sponsored Advanced Research Workshop on "Concepts in Electron Correlation" took place on the Croatian island of Hvar during the period from the 29th of September to the 3rd of October, 2002. The topic of electron correlation is a fundamental one in the field of condensed matter, and one that is being very actively studied both experimentally and theoretically at the present time. The manifestations of electron cor relation are diverse, and play an important role in systems ranging from high temperature superconductors, heavy fermions, manganite compounds with colossal magnetoresistance, transition metal compounds with metal insulator transitions, to mesoscopic systems and quantum dots. The aim of the workshop was to provide an opportunity for a dialogue between exper imentalists and theoreticians to assess the current state of understanding, and to set an agenda for future work. There was also a follow-up workshop on the same topic where the presentations included more background and introductory material for younger researchers in the field. The papers presented in these proceedings clearly demonstrate the di versity of current research on electron correlation. They show that real progress is being made in characterising systems experimentally and in developing theoretical approaches for a quantitative comparison with ex periment. The more one learns, however, the more there is to understand, and many of the contributions help to map out the territory which has yet to be explored. We hope that the articles in this volume will be a stimulus for such future work."

As concerns with the efficient use of energy resources, and the minimization of environmental damage have come to the fore, there has been a renewed interest in the role that thermoelectric devices could play in generating electricity from waste heat, enabling cooling via refrigerators with no moving parts, and many other more specialized applications. The main problem in realizing this ambition is the rather low efficiency of such devices for general applications. This book deals with the proceedings of a workshop addressed that problems by reviewing the latest experimental and theoretical work on suitable materials for device applications and by exploring various strategies that might increase their efficiency.

The proceedings cover a broad range of approaches, from the experimental work of fabricating new compounds through to theoretical work in characterizing and understanding their properties. The effects of strong electron correlation, disorder, the proximity to metal-insulator transitions, the properties of layered composite materials, and the introduction of voids or cages into the structure to reduce the lattice thermal conductivity are all explored as ways of enhancing the efficiency of their use in thermoelectric devices.

In recent years, there have been important developments in the design and fabrication of new thermoelectrics. While a decade ago, progress was mainly empirical, recent advances in theoretical methods have led to a deeper understanding of the parameters that affect the performance of materials in thermoelectric devices. These have brought the goal of producing materials with the required characteristics for commercial application a significant step closer. A search for efficient materials requires a fully microscopic treatment of the charge and heat transport, and the aim of this book is to explain all thermoelectric phenomena from this modern quantum-mechanical perspective. In the first part on phenomenology, conjugate current densities and forces are derived from the condition that the rate of change of the entropy density of the system in the steady state is given by the scalar product between them. The corresponding transport coefficients are explicitly shown to satisfy Onsager's reciprocal relations. The transport equations are solved for a number of cases, and the coefficient of performance, the efficiency, and the figure of merit are computed. State-of-the-art methods for the solution of the transport equations in inhomogeneous thermoelectrics are presented. A brief account on how to include magnetization transport in the formalism is also given. In the second part, quantum mechanical expressions for the transport coefficients are derived, following the approach by Luttinger. These are shown to satisfy Onsager's relations by construction. Three lattice models, currently used to describe strongly correlated electron systems, are introduced: the Hubbard, the Falicov-Kimball, and the periodic Anderson model (PAM), and the relevant current density operators are derived for each of them. A proof of the Jonson-Mahan theorem, according to which all transport coefficients for these models can be obtained from the integral of a unique transport function multiplied by different powers of the frequency, is given. The third part compares theory and experiment. First for the thermoelectric properties of dilute magnetic alloys, where the theoretical results are obtained from poor man's scaling solutions to single impurity models. Then it is shown that the experimental data on heavy fermions and valence fluctuators are well reproduced by the transport coefficients computed for the PAM at low and high temperature. Finally, results obtained from first principles calculations are shown, after a short introduction to density functional theory and beyond. A number of useful appendices complete the book.

Thermoelectric devices could play an important role in making efficient use of our energy resources but their efficiency would need to be increased for their wide scale application. There is a multidisciplinary search for materials with an enhanced thermoelectric responses for use in such devices. This volume covers the latest ideas and developments in this research field, covering topics ranging from the fabrication and characterization of new materials, particularly those with strong electron correlation, use of nanostructured, layered materials and composites, through to theoretical work to gain a deeper understanding of thermoelectric behavior. It should be a useful guide and stimulus to all working in this very topical field.

As concerns with the efficient use of energy resources, and the minimization of environmental damage have come to the fore, there has been a renewed interest in the role that thermoelectric devices could play in generating electricity from waste heat, enabling cooling via refrigerators with no moving parts, and many other more specialized applications. The main problem in realizing this ambition is the rather low efficiency of such devices for general applications. This book deals with the proceedings of a workshop addressed that problems by reviewing the latest experimental and theoretical work on suitable materials for device applications and by exploring various strategies that might increase their efficiency.

The proceedings cover a broad range of approaches, from the experimental work of fabricating new compounds through to theoretical work in characterizing and understanding their properties. The effects of strong electron correlation, disorder, the proximity to metal-insulator transitions, the properties of layered composite materials, and the introduction of voids or cages into the structure to reduce the lattice thermal conductivity are all explored as ways of enhancing the efficiency of their use in thermoelectric devices.

The NATO sponsored Advanced Research Workshop on "Concepts in Electron Correlation" took place on the Croatian island of Hvar during the period from the 29th of September to the 3rd of October, 2002. The topic of electron correlation is a fundamental one in the field of condensed matter, and one that is being very actively studied both experimentally and theoretically at the present time. The manifestations of electron cor relation are diverse, and play an important role in systems ranging from high temperature superconductors, heavy fermions, manganite compounds with colossal magnetoresistance, transition metal compounds with metal insulator transitions, to mesoscopic systems and quantum dots. The aim of the workshop was to provide an opportunity for a dialogue between exper imentalists and theoreticians to assess the current state of understanding, and to set an agenda for future work. There was also a follow-up workshop on the same topic where the presentations included more background and introductory material for younger researchers in the field. The papers presented in these proceedings clearly demonstrate the di versity of current research on electron correlation. They show that real progress is being made in characterising systems experimentally and in developing theoretical approaches for a quantitative comparison with ex periment. The more one learns, however, the more there is to understand, and many of the contributions help to map out the territory which has yet to be explored. We hope that the articles in this volume will be a stimulus for such future work."