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arXiv · 1803.05517

Plaquette order in classical spin liquid stabilized by strong off-diagonal exchange

Preetha Saha·Zhijie Fan·Depei Zhang·Gia-Wei Chern
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Abstract

We report a new classical spin liquid in which the collective flux degrees of freedom break the translation symmetry of the honeycomb lattice. This exotic phase exists in frustrated spin-orbit magnets where a dominant off-diagonal exchange, the so-called $\Gamma$ term, results in a macroscopic ground-state degeneracy at the classical level. We demonstrate that the system undergoes a phase transition driven by thermal order-by-disorder at a critical temperature $T_c \approx 0.04 |\Gamma|$. At first sight, this transition reduces an emergent spherical spin-symmetry to a cubic one: spins point predominantly toward the cubic axes at $T < T_c$. However, this seems to simply restore the cubic symmetry of the $\Gamma$ model, and the non-coplanar spins remain disordered below $T_c$. We show that the phase transition actually corresponds to plaquette ordering of hexagonal fluxes and the cubic symmetry is indeed broken, a scenario that is further confirmed by our extensive Monte Carlo simulations.

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Preetha Saha, Zhijie Fan, Depei Zhang, Gia-Wei Chern. 2018-03-14. Plaquette order in classical spin liquid stabilized by strong off-diagonal exchange. https://doi.org/10.1103/physrevlett.122.257204

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