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In the group we investigate the theoretical aspects of materials where new, collective properties emerge due to strong interactions. Examples of such collective properties are magnetism, superconductivity and orbital ordering. Relevant materials are e.g. magnetic transition metal oxides, such as the Colossal Magneto-Resistance (CMR) manganites and high-Tc cuprate superconductors, but also molecular crystals such as intercalated C60 and metal-phtalocynanines. The physical properties of these solids are dominated by the effects of strong electron-electron interactions. We focus on the development and treatment of model Hamiltonians for these many-body systems, and seek to relate theoretical results to experimental observations.
At present we have four research projects in the group:
Orbital physics
We know that orbital degrees of freedom have large effects on optical, transport and magnetic properties, but in many cases a basic understanding of such effects is lacking. This is the motivation to study orbital ordering, orbital excitations and the coupling of orbitals to lattice, spin and charge in general. The results we apply to, for instance, the CMR manganites.
Group members involved:
JvdB (Principle Investigator),
Edmundo Sanchez (PhD student),
N.N. (Post-doc)
Collaboration with: Prof. Dr. Daniel Khomskii (Cologne University, Germany), Prof. Dr. Giniyat Khaliullin (Max-Planck-Institute, Stuttgart, Germany), Prof. Dr. Mikhail Katsnelson (Radboud University, Nijmegen, NL).
Organic semi-conductors
Recent experimental progress in the field of molecular crystals motivated us to investigate electron correlation effects, magnetism and electric field effects in organic crystals of e.g. pentacene, thiophenes and alkali doped metal-phtalocyanines.
Group members involved:
JvdB (PI),
Gianluca Giovanetti (PhD student), Jorrit Glastra (MSc student)
Collaboration with: Dr. Alberto Morpurgo (experiment, Technical University Delft, NL), Prof. Dr. Paul Kelly and Dr. Geert Brocks (both University of Twente, NL).
Resonant Inelastic X-ray Scattering (RIXS)
Hard X-ray RIXS is a powerful new technique that is rapidly developing at the synchrotron facilities in e.g. Chicago and Brookhaven. We are following these developments from the theoretical side by determining which physical correlation functions are actually measured in RIXS and by calculating them.
Group members involved:
JvdB (PI)
Collaboration with: Prof. Dr. Michel van Veenendaal (Argonne National Laboratory, USA) and Dr. John Hill (experiment, Brookhaven National Laboratory, USA)
Quantum computation and decoherence
We study the relationship between spontaneous symmetry breaking and quantum coherence by means of exactly solvable spin models. The aim is, on one hand, to obtain a fundamental understanding of quantum decoherence without invoking extrinsic dissipation and to construct decoherence-free subspaces for qubits. On the other hand we strive to provide a clear-cut computation of symmetry breaking related decoherence rates of experimentally realizable many-particle qubits.
Group members involved:
JvdB (PI),
Jasper van Wezel (PhD student)
Collaboration with: Prof. Dr. J. Zaanen (Leiden, NL) and Prof. Dr. Philip Stamp (UBC, Vancouver, Canada)
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