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arXiv · 2402.05693

NMR evidence of spinon localization in kagome antiferromagnet YCu$_3$(OH)$_6$Br$_2$[Br$_{1-x}$(OH)$_x$]

Shuo Li·Yi Cui·Zhenyuan Zeng·Yue Wang·Ze Hu·Jie Liu·Cong Li·Xiaoyu Xu·Ying Chen·Zhengxin Liu·Shiliang Li·Weiqiang Yu
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Abstract

We performed nuclear magnetic resonance studies on a kagome antiferromagnet YCu$_3$(OH)$_6$Br$_2$[Br$_{1-x}$(OH)$_{x}$]. No significant NMR spectral broadening is found in the Br center peak from 1 K down to 0.05 K, indicating absence of static antiferromagnetic ordering. In contrast to signatures of dominant 2D kagome antiferromagnetic fluctuations at temperature above 30 K, both the Knight shift $K_{\rm{n}}$ and the spin-lattice relaxation rate $1/T_{1}$ increase when the sample is cooled from 30 K to 8 K, which can be attributed to the scattering of spin excitations by strong non-magnetic impurities. Unusually, a hump is observed in $K_{\rm{n}}$ and $1/T_{2}$ close to 2 K (far below the exchange energy), which indicates the existence of excitations with a large density of states close to zero energy. These phenomena are reproduced by a mean-field simulation of Heisenberg model with bond-dependent exchange interactions, where the sign fluctuations in the spinon kinetic terms caused by impurities result in localization of spinons and an almost flat band close to the Fermi energy.

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Shuo Li, Yi Cui, Zhenyuan Zeng, Yue Wang, Ze Hu, Jie Liu, Cong Li, Xiaoyu Xu, Ying Chen, Zhengxin Liu, Shiliang Li, Weiqiang Yu. 2024-02-08. NMR evidence of spinon localization in kagome antiferromagnet YCu$_3$(OH)$_6$Br$_2$[Br$_{1-x}$(OH)$_x$]. https://doi.org/10.1103/physrevb.109.104403

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