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TT: Fachverband Tiefe Temperaturen

TT 55: Low-Dimensional Systems: 2D – Theory

TT 55.11: Vortrag

Mittwoch, 18. März 2015, 12:15–12:30, H 3010

Mott physics in the half-filled Hubbard model on a family of vortex-full square lattices — •Dominik Ixert¹, Fakher Assaad², and Kai Phillip Schmidt¹ — ¹Lehrstuhl für Theoretische Physik 1, TU Dortmund, D-44221 Dortmund, Germany — ²Institut für Theoretische Physik und Astrophysik, Universität Würzburg, Am Hubland, D-97074 Würzburg, Germany

We study the half-filled Hubbard model on a one-parameter family of vortex-full square lattices ranging from the isotropic case to weakly coupled Hubbard dimers. The ground-state phase diagram consists of four phases: A semimetal and a band insulator which are connected to the weak-coupling limit, and a magnetically ordered Néel phase and a valence bond solid (VBS) which are linked to the strong-coupling Mott limit. The phase diagram is obtained by quantum Monte Carlo (QMC) and continuous unitary transformations (CUTs). The CUT is performed in a two-step process: Nonperturbative graph-based CUTs are used in the Mott insulating phase to integrate out charge fluctuations. The resulting effective spin model is tackled by perturbative CUTs about the isolated dimer limit yielding the breakdown of the VBS by triplon condensation. We find three scenarios when varying the interaction for a fixed anisotropy of hopping amplitudes: (i) one direct phase transition from Néel to semimetal, (ii) two phase transitions VBS to Néel and Néel to semimetal, or (iii) a smooth crossover from VBS to the band insulator. Our results are consistent with the absence of spin-liquid phases in the whole phase diagram.

[1] D. Ixert, F. F. Assaad, and K. P. Schmidt,

PRB 90, 195133 (2014).