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TT: Fachverband Tiefe Temperaturen

TT 94: Correlated Magnetism – Low-Dimensional Systems

TT 94.7: Talk

Friday, March 13, 2026, 11:15–11:30, HSZ/0101

Symmetry-Protected Topological Phase Diagrams of Dimerized Heisenberg Ladders — Tim Obrock and •Anas Abdelwahab — Leibniz Universität Hannover, Institute für Theoretische Physik, Hannover, Germany

We present symmetry-protected topological phase diagrams of unfrustrated dimerized spin-1/2 ladders with perpendicular (J_⊥) and diagonal (J_d) rung couplings, studied as a function of dimerization (δ) and inter-wire coupling strength. For two perpendicularly coupled wires, our results reproduce the established picture from previous studies: antiferromagnetic rungs yield a trivial spin-0 phase, while ferromagnetic rungs drive the system into the Haldane symmetry-protected topological phase at small |δ|, with critical lines converging to the dimerized spin-1 chain limit for J_⊥ ≪ −1.

For three perpendicularly coupled wires, earlier work has shown that antiferromagnetic rungs drive a transition from trivial (δ > 0) to Haldane (δ < 0). Under ferromagnetic rungs, the system approaches the dimerized spin-3/2 chain limit for J_⊥ ≪ −1, exhibiting a sequence of trivial*Haldane*trivial*Haldane phases as δ evolves from 1 to −1.

Extending beyond these previous studies, we analyze the case of two and three diagonally coupled wires. For two wires, antiferromagnetic rungs produce a Haldane region bounded by |δ| ≈ J_d/2, containing the exact spin-1 chain limit at J_d = 1 and δ = 0, while ferromagnetic rungs keep the system trivial. For three diagonally coupled wires, our results reveal a phase diagram with trivial and topological phases but without an apparent spin-chain limit.

Keywords: Symmetry Protected Toplogical Phases; Hesienberg Ladders