Berlin 2024 – scientific programme

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TT: Fachverband Tiefe Temperaturen

TT 27: Correlated Electrons: Other Materials

TT 27.12: Talk

Tuesday, March 19, 2024, 12:30–12:45, H 3010

Phases and Exotic Phase Transitions of a Two-Dimensional Su-Schrieffer-Heeger Model — •Anika Götz¹, Martin Hohenadler¹, and Fakher Assaad^{1, 2} — ¹Institut für Theoretische Physik und Astrophysik, Universität Würzburg, 97074 Würzburg, Germany — ²Würzburg-Dresden Cluster of Excellence ct.qmat, Am Hubland, 97074 Würzburg, Germany

We study a Su-Schrieffer-Heeger electron-phonon model on a square lattice with auxiliary-field quantum Monte Carlo simulations. Adding a symmetry-allowed interaction permits analytical integration over the phonons at the expense of discrete Hubbard-Stratonovich fields with imaginary-time correlations. We investigate the phase diagram at the O(4)-symmetric point as a function of hopping t and phonon frequency ω₀. For t=0, where electron hopping is boson-assisted, the model maps onto an unconstrained Z₂ gauge theory. A key quantity is the emergent effective flux per plaquette, which equals π in the assisted-hopping regime and vanishes for large t. Phases in the former regime can be understood in terms of instabilities of emergent Dirac fermions. Our results support a direct and continuous transition between a (π,0) valence bond solid (VBS) and an antiferromagnetic (AFM) phase with increasing ω₀. By increasing the electronic interaction the critical phonon frequency can be lowered, driving the transition to a first order one. In addition the role of doping away from half-filling is studied. For large t and small ω₀, we find finite-temperature signatures of a previously reported (π,π) VBS ground state related to a nesting instability. With increasing ω₀, AFM order again emerges.

Keywords: Su-Schrieffer-Heeger model; Quantum Monte Carlo; Electron-phonon coupling