Spin-orbital entanglement and dynamic properties of spin-orbital systems

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In transition metal oxides, quantum effects and correlations between electrons lead to a large variety of material properties. While they can in some cases be described by one-band models where the only relevant properties of the electrons are their spin and charge, some materials have another degree of freedom: the orbital occupied by the electron. With strong Coulomb repulsion, this leads to spin-orbital physics, where spin and orbital degrees of freedom are entangled. I propose to calculate dynamic susceptibilities for realistic models describing spin-orbital systems. Such calculations are necessary to describe and understand experiments like angle resolved photoemission spectroscopy (ARPES) or neutron scattering and also give information about fundamental excitations. While analytic methods exist for special cases in one dimension, I propose to use numerical methods based on exact diagonalization and cluster-embedding, especially the variational cluster approach. They can be applied to more general and realistic models and can also be used in higher dimensions. Recently, superconductivity has been investigated in iron-pnictides, where several bands cross the Fermi energy, suggesting that the orbital degree of freedom is relevant. The proposed project also includes work on orbital models for pnictides and on the temperature dependence of the magnetic susceptibility.