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TT 71.6: Vortrag
Freitag, 20. März 2020, 11:00–11:15, HSZ 304
Nonlocal Exchange Interactions in Strongly Correlated Electron Systems — •Edin Kapetanović1,2, Malte Schüler1,2, Gerd Czycholl1, and Tim Wehling1,2 — 1Institut für Theoretische Physik, Universität Bremen — 2Bremen Center for Computational Materials Science, Universität Bremen
We study the influence of ferromagnetic nonlocal exchange on correlated electrons in terms of a SU(2)-Hubbard-Heisenberg model and address the interplay of on-site interaction induced local moment formation and the competition of ferromagnetic direct and antiferromagnetic kinetic exchange interactions. In order to simulate thermodynamic properties of the system in a way that largely accounts for the on-site interaction driven correlations, we advance the correlated variational scheme introduced in [M. Schüler et al., Phys. Rev. Lett. 111, 036601 (2013)] to account for explicitly symmetry broken electronic phases by introducing an auxiliary magnetic field. After benchmarking the method against exact solutions of a finite system, we study the SU(2)-Hubbard-Heisenberg model on a square lattice. We obtain the U-J finite temperature phase diagram of a SU(2)-Hubbard-Heisenberg model within the correlated variational approach and compare to static mean field theory (MFT). While the generalized variational principle and MFT yield similar transitions, we find that the nature of the associated phase transitions differs between the two approaches. The fluctuations accounted for in the variational approach render the transitions continuous, while MFT predicts discontinuous transitions between ferro- and antiferromagnetically ordered states.