SKM 2021 – wissenschaftliches Programm

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TT: Fachverband Tiefe Temperaturen

TT 18: Frustrated Magnets

TT 18.4: Vortrag

Donnerstag, 30. September 2021, 10:45–11:00, H7

Two-triplon excitations in frustrated bilayer systems — •Erik Wagner and Wolfram Brenig — Institute for Theoretical Physics, Technical University Braunschweig, Braunschweig, Germany

We study the magnetism of frustrated bilayer spin models. Starting from the limit of decoupled dimers we use the perturbative continuous unitary transformation (pCUT), based on the flow equation method, to perform series expansion in order to analyze the spectrum, up to the two-triplon excitations. First we apply this method to the Kitaev-Heisenberg bilayer, consisting of two honeycomb Kitaev spin-models with anisotropic intralayer Ising-exchange J_x,y,z, coupled by additional interlayer Heisenberg exchange J. We evaluate the groundstate energy and the one particle dispersion up to 9th order in J_x,y,z as well as the two-particle interactions and spectrum up to 6th order [1]. We detail the presence of (anti-)bound two-particle states and analyze their wavefunctions. Additionally we discuss the impact of two-particle interactions on the magnetic Raman response of the Kitaev-Heisenberg bilayer. Extensions of our approach to other frustrated bilayers will be considered, focusing on the SU(2) invariant J-J₁-J₂-Heisenberg square-lattice bilayer and including calculations up to 7th and 4th order in J_1,2 for one- and two-particle matrix elements.
[1] E. Wagner, W. Brenig, arXiv:2103.13402