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TT: Fachverband Tiefe Temperaturen

TT 23: Frustrated Magnets - General

TT 23.8: Vortrag

Mittwoch, 7. September 2022, 17:00–17:15, H22

One- and two-particle dynamics of the J₁-J₂-Heisenberg bilayer — •Erik Wagner and Wolfram Brenig — TU Braunschweig, Braunschweig, Germany

The antiferromagnetic J₁-J₂ Heisenberg-model on the square lattice is one of the pillars of frustrated quantum magnetism, with Néel- and collinearly ordered ground states competing for large and small J₁/J₂, and with a quantum disordered phase of still unsettled nature in between. Probing fingerprints of such phases by approaching them out of a well controlled dimer phase is one of the rationals for studying bilayer versions of frustrated spin models. Here, and 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 of the square lattice J₁-J₂-Heisenberg bilayer up to the two-triplon excitations. Evaluating the ground state energy and the one-particle dispersion up to 7th order in J_1,2 as well as the two-particle interactions and spectrum up to 5th order, we find emerging (anti-)bound two-particle states, which can be classified by total spin and real-space symmetry, consistent with results found for the J₁-only bilayer on the square lattice [1]. We analyze the phase boundary of the dimer phase with respect to one- and two-particle excitations and find reasonable agreement with recent coupled-cluster calculations [2], while also uncovering prospects for an additional phase introduced by two-particle boundstate condensation.

[1] A. Collins, C.J. Hamer, PRB 78, 054419 (2008)

[2] R.F. Bishop et al., PRB 100, 024401 (2019)