Phenomenology of high-temperature superconducting cuprates: microscopic approach from weak coupling

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This project proposal contains three sub-projects. In the first two sub-projects, two important issues of the physics of high-temperature superconductors, the nature of the pseudogap in underdoped systems and the role of lattice vibrations, will be addressed theoretically using functional renormalization group techniques. This approach is well-founded for weak to moderate interactions and is capable to treat competing interactions on equal footing. Our aim is to obtain qualitative insights which can be used to understand the experimental phenomenology and to help interpreting results of other, more involved theoretical approaches at stronger interactions. Respective examples are ans¨atze for a better characterization of spectral data in the pseudogap regime and the mutual interactions between spin fluctuations and different types of phonons. In a third sub-project, the combination of Quantum Monte-Carlo and functional renormalization group techniques shall be developed with the goal to extend the above-mentioned description toward stronger interactions.