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TT: Fachverband Tiefe Temperaturen
TT 94: Correlated Magnetism – Low-Dimensional Systems
TT 94.8: Talk
Friday, March 13, 2026, 11:30–11:45, HSZ/0101
Self-consistent mean-field theory and continuous unitary transformations for ordered quantum antiferromagnets with long-range interactions — •Maximilian Bayer1, Dag-Björn Hering2, Vanessa Sulaiman2, Götz Uhrig2, and Kai Schmidt1 — 1Department of Physics, Friedrich-Alexander-Universität Erlangen-Nürnberg, Erlangen, Germany — 2Condensed Matter Theory, Technische Universität, Dortmund, Germany
We investigate the antiferromagnetic Heisenberg model on a square lattice in the presence of algebraically decaying long-range interaction. The model is first studied using a fully self-consistent mean-field treatment going beyond linear spin-wave theory. We discuss the challenges and solutions to obtain numerical results of these long-range interacting systems using functional self-consistency equations familiar to the superconducting gap equation and a parametrisation using Epstein-zeta functions to capture the long-range behaviour without truncation in the system size. In a next step we go beyond the mean-field level and apply continuous similarity transformations (CST) in momentum space. The associated flow equations are truncated in the scaling dimension to capture consistently quantum fluctuations in the ordered phase in the same manner as for the case of nearest-neighbor interactions [1]. Our aim is to understand the one-magnon dispersion at low and high energies including the fate of the characteristic roton minimum.
[1] M. Powalski, G.S. Uhrig, K.P. Schmidt, PRL 115, 207202 (2015)
Keywords: Long-range interaction; Mean-field; Heisenberg; Quantum Antiferromagnet; Magnon