Dresden 2026 – scientific programme

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TT: Fachverband Tiefe Temperaturen

TT 31: Frustrated Magnets I (joint session MA/TT)

TT 31.1: Talk

Tuesday, March 10, 2026, 09:30–09:45, POT/0361

Spontaneous symmetry breaking in the Heisenberg antiferromagnet on a triangular lattice — •Bastian Pradenas^1,2, Grigor Adamyan^1,3, and Oleg Tchernyshyov¹ — ¹William H. Miller III Department of Physics and Astronomy, Johns Hopkins University, Baltimore, USA — ²Leibniz Institute for Solid State and Materials Research, IFW, Dresden, Germany — ³Department of Physics, Massachusetts Institute of Technology, Cambridge, USA

We present a detailed investigation of an overlooked symmetry structure in non-collinear antiferromagnets that gives rise to an emergent quantum number for magnons. Focusing on the triangular-lattice Heisenberg antiferromagnet, we show that its spin order parameter transforms under an enlarged symmetry group, SO(3)_L × SO(2)_R, rather than the conventional spin-rotation group SO(3). Although this larger symmetry is spontaneously broken by the ground state, a residual subgroup survives, leading to conserved Noether charges that, upon quantization, endow magnons with an additional quantum number—isospin—beyond their energy and momentum. Our results provide a comprehensive framework for understanding symmetry, degeneracy, and quantum numbers in non-collinear magnetic systems, and bridge an unexpected connection between the paradigms of symmetry breaking in non-collinear antiferromagnets and chiral symmetry breaking in particle physics.

Keywords: Frustrated Magnetism; Antiferromagnetism; Noncollinear; Triangular Lattice; Magnons