The Nobel prize winner P.W. Anderson1 describes with the words "more is different" how the interplay of many constituents in a solid can lead to qualitatively new effects and material properties. An important challenge of modern solid state physics and of this special research program SFB608 is the discovery and investigation of such collective phenomena.
The subject of the special research program SFB608 is complex transition metal compounds. Their manifold and fascinating properties are due to the flexible electronic structure of transition metal ions and to the strong interaction of the resulting spin, charge and orbital degrees of freedom. The collective interplay of these modules creates a huge number of new phenomena and material states.
In transition metal compounds, metallic and insulating phases, superconductivity, magnetism, ferroelectricity, orbital order and also spontaneous lattice distortions are often close to one another. The investigation of systems where different degrees of freedom or different interactions of phases are influencing or competing with one another is a particularly promising way to discover materials with new properties, possibly of technical interest, and new states of matter. These type of systems often react very sensitively to small changes of their environment and have therefore a large potential as sensors, actuators or storage media. For example, in multiferroics magnetic and ferroelectric properties are coupled so that magnetic domains can be switched electrically. Or it might happen that a third phase (e.g. a superconducting one) is stabilized when two different states are competing (e.g. a magnetic and metallic one). The critical fluctuations which go along with a phase transition can lead to anomalous material properties if the transition takes place at zero temperature and they can be described by new particles with exotic properties.
The SFB608 synthesizes and characterizes new transition metal compounds in a close collaboration between physics, inorganic chemistry and crystallography. A large variety of spectroscopic techniques complements thermodynamic and transport measurements and allows, in combination with model calculations, the elucidation of the basic properties of correlated transition metal systems and the observation of the elementary excitations in these materials.
In addition the SFB608 emphasizes the promotion of young scientists, gender affairs and the reconciliation of family and work life. Here the SFB608 works closely together with existing structures of the University of Cologne and the Bonn-Cologne Graduate School of Physics and Astronomy (BCGS). The latter is funded since 2007 through the excellence initiative of the Federal Government.
1 P. W. Anderson, Science 177, 393 (1972)