Dresden 2026 – scientific programme
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TT: Fachverband Tiefe Temperaturen
TT 35: Cooperative Phenomena: Spin Structures and Magnetic Phase Transitions (joint session MA/TT)
TT 35.3: Talk
Tuesday, March 10, 2026, 14:30–14:45, POT/0151
Transition between critical antiferromagnetic phases in the J1-J2 spin chain — Adam McRoberts1, •Chris Hooley2, and Andrew Green3 — 1International Centre for Theoretical Physics, Trieste, Italy — 2Coventry University, Coventry, United Kingdom — 3University College London, London, United Kingdom
The J1-J2 spin chain is one of the canonical models of quantum magnetism, and has long been known to host a critical antiferromagnetic phase with power-law decay of spin correlations. We show that there are, in fact, two distinct critical antiferromagnetic phases, where the roles of the local dimer field and its dual field are interchanged: the 'Affleck-Haldane' phase near the Heisenberg point J2 = 0, where the dimer field that parametrises local singlet order is gapless and part of a joint O(4) Neel-singlet order parameter; and the 'Zirnbauer' phase which appears at sufficiently large ferromagnetic J2, where the dimer field is gapped out and its dual field - the instanton density of the O(3) Neel field - is critical instead. The phases are so-named because each realises one of the competing pictures for how the O(3) non-linear sigma model with a topological theta term renormalises to the su(2) level 1 Wess-Zumino-Witten model. We support these predictions with density matrix renormalisation group calculations.
Keywords: Spin chain; Luttinger liquid; Quantum phase transition