University of Cambridge > Department of Physics. Cavendish Laboratory > Theory of Condensed Matter > CoMePhS

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Max Plank Institute for Solid State Research Contact: Annette Bussmann-Holder (A.Bussmann-Holder at fkf.mpg.de) Our research is titled: Polaron Formation and Unconventional Lattice Effects in Complex Perovskite Oxides Link to Conference being organized: March 27 - 29, 2006 The main focus of the current activities is on high temperature superconductivity in cuprates and in MgB2 and doped MgB2. While for cuprates the observed heterogeneity is modeled within a two-component scenario, where T* signals the onset of self-organized pattern formation, MgB2  is more conventional, however, with the distinction as compared to standard BCS superconductors that it exhibits two gaps. In both systems isotope effects are poorly understood and will be investigated in the future. In addition unconventional lattice effects in terms of intermediate sized polarons will be investigated in order to understand the local deviations from the average crystallographic structure as observed in cuprates. It is important here, to identify the lattice distortion which couples most strongly to the electronic structure. Another focus lies on ferroelectrics, displacive ones as well as relaxor ferroelectrics. While the former ones  can be described in terms of local Phi-4 potentials, relaxors are still poorly understood from a  microscopic point of view. In these systems a broad distribution in relaxation times evidences intrinsic heterogeneity which should relate to various measurable properties. Interesting is in this context, that extremely high and temperature stable dielectric constants are observed. Over the next year we hope to: Calculate unconventional isotope effects as observed in cuprates, calculate their phase diagram, and study competing or coexisting phases like the pseudogap phase and the SC phase. Calculation of the thermoelectric power which shows various crossover temperatures which are partially unrelated to the pseudogap or SC phase. Model relaxors within nonlinear concepts with the focus of finding solutions which are limited to a few lattice constants. Study of possible mechanisms which explain the largely increased and stable dielectric constants. Please see our web-site www.fkf.mpg.de

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