Spin nematics in spin-1/2 antiferromagnets next to spin singlet phase

Orateur : Chisa HOTTA (Department of Basic Science, University of Tokyo)

Spin nematics in spin-1/2 systems is known to appear mostly either at high fields or in the vicinity of a ferromagnetic phase. There, two magnon excitations in those fully polarized nearby phases form bound states and condense and form a quadrupolar order[1]. We propose instead a different mechanism to have spin nematics in the vicinity of spin singlet phase — a trivial phase of spin-1/2 antiferromagnet based on a dimer structure[2]. We show that the ring exchange interaction that connect pairs of spins belonging to different dimers generate a spin-1 biquadratic interaction term, which is responsible for the emergent spin nematics. The Bose Einstein condensate(BEC) of SU(2) triplets is also observed \ itwithout a magnetic field, which is the one that could be discriminated from the magnon BEC, and further, the coexistence of BEC and spin nematics is observed in this kind of simple toy model.

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