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### arXiv:1909.04647 [cond-mat.str-el]AbstractReferencesReviewsResources

#### Spin nematic phases driven by the Heisenberg interactions in a spin-1 dimer system forming a bilayer

Published 2019-09-10Version 1

Spin nematics had long been considered as an elusive nonmagnetic state, where the spin-1 moments lose their directions while keeping the orientations in a spatially ordered manner similar to the liquid crystals. Such order emerges as a result of transverse fluctuation of spin-1 moments, which is enhanced by the quantum many body effect. We propose a realistic model system based on dimers forming bilayers that can easily host spin nematics. Each dimer consists of antiferromagnetically coupled spin-1 pair which tend to form a dimer-singlet phase. We show that this dimer-singlet is immediately replaced with the ferroic nematic phases, when very small inter-dimer Heisenberg exchange interactions are introduced. This nematics is exotic in the sense that the spin-1 moments form a uniform Bose--Einstein condensate, whereas the nematic directors develop a spatially modulated structure. It apparently differs from the conventional ones found in a strong magnetic field or next to the ferromagnetic phases, which were often difficult to realize in experiments. Hidden nematic phases should thus exist in many of the quantum spin-dimer materials, which serve as a good platform to study nematic phases in laboratories, and a family of Ba$_{3}$ZnRu$_{2}$O$_{9}$ may become a first possible example.

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