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MA: Fachverband Magnetismus
MA 28: Frustrated Magnets - Spin Liquids 2 (joint session TT/MA)
MA 28.1: Vortrag
Dienstag, 17. März 2020, 14:00–14:15, HSZ 304
Theory of partial quantum disorder in the stuffed honeycomb Heisenberg antiferromagnet — •Urban F. P. Seifert and Matthias Vojta — Institut für Theoretische Physik and Würzburg-Dresden Cluster of Excellence ct.qmat, Technische Universität Dresden, 01062 Dresden, Germany
Recent numerical results [Gonzalez et al., Phys. Rev. Lett. 122, 017201 (2019); Shimada et al., J. Phys. Conf. Ser. 969, 012126 (2018)] point to the existence of a partial-disorder ground state for a spin-1/2 antiferromagnet on the stuffed honeycomb lattice, with 2/3 of the local moments ordering in an antiferromagnetic Néel pattern, while the remaining 1/3 of the sites display short-range correlations only, akin to a quantum spin liquid.
In this talk, we derive an effective model for this disordered subsystem, by integrating out fluctuations of the ordered local moments, which yield couplings in a formal 1/S expansion, with S being the spin amplitude. The result is an effective triangular-lattice XXZ model, with planar ferromagnetic order for large S and a stripe-ordered Ising ground state for small S, resulting from frustrated Ising interactions. Within semiclassical analysis, the transition point between the two orders is located at Sc=0.646, being very close to the relevant case S=1/2. Near S=Sc quantum fluctuations tend to destabilize magnetic order. We conjecture that this applies to S=1/2, thus explaining the observed partial-disorder state.