In interacting many-particle systems such as electrons in solids, the concept of a single, elementary particle loses its meaning. In spite of well-known interactions between the particles completely new and surprising phenomena such as phase transitions can emerge. In this context the term "electronic correlations" plays an important role. It refers to effects of the interaction between the particles which cannot be explained by viewing the interaction as a mean field. Electronic correlations influence the electronic and magnetic properties of matter strongly. In my talk，I will present a basic introduction into the concepts of correlated electronic systems. In particular, I will describe recent theoretical progress which allows one to go beyond the investigation of simple models and thereby explain properties of correlated electron materials.
Professor Dieter Vollhardt studied physics from 1971 to 1975 in University of Hamburg. He then spent 3 years in University of southern California in Los Angeles with Prof. Maki. He obtained his diploma degree in 1977 and within less one year, his doctoral degree in 1978. The topic of his doctoral thesis is “The superfluid phase of He 3”. From 1977 to 1984, he did his postdoc research with Prof. Peter Woelfle at Max-Planck institute for Physics and Astrophysics (also known as Werner Heisenberg institute) in Munich. He finished his Habilitation in 1984 on the topic of “Theoretical investigation of correlated Fermionic systems: liquid He 3 and disordered metals”. From 1984 to 1987, he became a Heisenberg Fellow of German Physical Society at the same institute. In 1987, at an age of 36, Professor Vollhardt became a chair professor and the director of institute of physics at Aachen Institute of Technology, where he worked there until 1996. In 1996 he accepted a position of chair professor in University of Augsburg, and build the center of electron correlation and magnetism there. He has been working there ever since. Over the years, Professor Vollhardt has done influential work in several different areas and problems. The focus is however, always on correlation problem, both for fermionic and bosonic systems. His most well-known contribution is the development and application of the dynamical mean-field theory, which is now a widely used powerful tool to deal with strongly correlated systems. He received the Europhysical prize in 2006, together with Anton Georges, Gabi Kotliar, and Walter Metzner, “for the development of application of the dynamical mean-field theory”, the Max-Planck metal in 2010 “in recognition of his significant contributions to the derivation of a new mean-field theory of correlated quantum systems and to the understanding of many-body problems in the quantum theory of condensed matter”, and the Ernst-Mach medal in 2011 “for merit of physical sciences”.