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Nisheeta Desai (TIFR, Mumbai)
Date & Time
Wed, 13 September 2023, 15:00 to 16:30
Madhava Lecture Hall and Online

Berry phase interference arguments that underlie the theory of deconfined quantum criticality (DQC) for spin-1/2 antiferromagnets have also been invoked to allow for continuous transitions in spin-1 magnets including a Néel to (columnar) valence bond solid (cVBS) transition. We provide a microscopic model realization of this transition on the square lattice consisting of Heisenberg exchange (J_H) and biquadratic exchange (J_B) that favor a Néel phase, and a designed Q-term (Q_B) interaction which favors a cVBS through large-scale quantum Monte Carlo (QMC) simulations. For J_H=0, this model is equivalent to the SU(3) JQ model with a Néel-cVBS transition that has been argued to be DQC through QMC. Upon turning on J_H which brings down the symmetry to SU(2), we find multiple signatures -- a single critical point, high quality collapse of correlation ratios and order parameters, "U(1)-symmetric" cVBS histograms and lack of double-peak in order parameter histograms for largest sizes studied near the critical point -- that are highly suggestive of a continuous transition scenario. However, Binder analysis finds negative dips that grow sub-extensively that we interpret as these transitions rather being pseudocritical. This along with recent results on spin-1/2 models suggests that deconfined pseudocriticality is the more generic scenario.

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