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arXiv · 1911.06492

Strain-induced spin-nematic state and nematic susceptibility arising from $2\times2$ Fe clusters in KFe$_{0.8}$Ag$_{1.2}$Te$_2$

Yu Song·Dongsheng Yuan·Xingye Lu·Zhijun Xu·Edith Bourret-Courchesne·Robert J. Birgeneau
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Abstract

Spin nematics break spin-rotational symmetry while maintaining time-reversal symmetry, analogous to liquid crystal nematics that break spatial rotational symmetry while maintaining translational symmetry. Although several candidate spin nematics have been proposed, the identification and characterization of such a state remain challenging because the spin-nematic order parameter does not couple directly to experimental probes. KFe$_{0.8}$Ag$_{1.2}$Te$_2$ (K$_5$Fe$_4$Ag$_6$Te$_{10}$, KFAT) is a local-moment magnet consisting of well-separated 2$\times$2 Fe clusters, and in its ground state the clusters order magnetically, breaking both spin-rotational and time-reversal symmetries. Using uniform magnetic susceptibility and neutron scattering measurements we find a small strain induces sizable spin anisotropy in the paramagnetic state of KFAT, manifestly breaking spin-rotational symmetry while retaining time-reversal symmetry, resulting in a strain-induced spin-nematic state in which the $2\times2$ clusters act as the spin analogue of molecules in a liquid crystal nematic. The strain-induced spin anisotropy in KFAT allows us to probe its nematic susceptibility, revealing a divergent-like increase upon cooling, indicating the ordered ground state is driven by a spin-orbital entangled nematic order parameter.

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Yu Song, Dongsheng Yuan, Xingye Lu, Zhijun Xu, Edith Bourret-Courchesne, Robert J. Birgeneau. 2019-11-15. Strain-induced spin-nematic state and nematic susceptibility arising from $2\times2$ Fe clusters in KFe$_{0.8}$Ag$_{1.2}$Te$_2$. https://doi.org/10.1103/physrevlett.123.247205

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