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

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 $K_{\mathrm{n}}$ 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 $K_{\mathrm{n}}$ 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.

9 pages, 7 figures. The supplementary materials can be obtained upon request

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Cited by in corpus (7)

• Magnetic ground states in kagome YCu${}_3$(OH)${}_6$[(Cl${}_x$Br${}_{1-x}$)${}_{3-y}$(OH)${}_y$]
• Thermodynamic evidence of fermionic behavior in the vicinity of one-ninth plateau in a kagome antiferromagnet
• Chemo-Structural Disorder in the kagomé spin $S$ = 1/2 systems ZnCu${}_3$(OH)${}_6$Cl${}_2$ and YCu${}_3$(OH)${}_6$Br${}_2$[Br${}_x$(OH)${}_{1-x}$]
• Magnetic excitations in the 1/3 plateau state in InCu${}_3$(OH)${}_6$Cl${}_3$
• Spin excitations arising from anisotropic Dirac spinons in YCu${}_3$(OD)${}_6$Br${}_2$[Br${}_{0.33}$(OD)${}_{0.67}$]
• Exerting chemical pressure on the kagome lattice as frustration control in the kapellasite family $A$Cu${}_3$(OH)${}_{6+x}$(Cl,Br)${}_{3-x}$
• Spiral spin liquid resilient to quantization in the frustrated honeycomb antiferromagnet GdZnPO