Possible Dirac quantum spin liquid in the kagome quantum antiferromagnet <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:msub><mml:mi>YCu</mml:mi><mml:mn>3</mml:mn></mml:msub><mml:msub><mml:mrow><mml:mo>(</mml:mo><mml:mi>OH</mml:mi><mml:mo>)</mml:mo></mml:mrow><mml:mn>6</mml:mn></mml:msub><mml:msub><mml:mi>Br</mml:mi><mml:mn>2</mml:mn></mml:msub><mml:mrow><mml:mo>[</mml:mo><mml:msub><mml:mi>Br</mml:mi><mml:mi>x</mml:mi></mml:msub><mml:msub><mml:mrow><mml:mo>(</mml:mo><mml:mi>OH</mml:mi><mml:mo>)</mml:mo></mml:mrow><mml:mrow><mml:mn>1</mml:mn><mml:mo>−</mml:mo><mml:mi>x</mml:mi></mml:mrow></mml:msub><mml:mo>]</mml:mo></mml:mrow></mml:mrow></mml:math>
Zhenyuan Zeng, Xiaoyan Ma, Si Wu, Haifeng Li, Zhen Tao, Xingye Lu, Xiao-hui Chen, Jin‐Xiao Mi, Shijie Song, Guang‐Han Cao, Guangwei Che, Kuo Li, Gang Li, Huiqian Luo, Zi Yang Meng, Shiliang Li
Abstract
We studied the magnetic properties of ${\mathrm{YCu}}_{3}{(\mathrm{OH})}_{6}{\mathrm{Br}}_{2}[{\mathrm{Br}}_{1\ensuremath{-}x}{(\mathrm{OH})}_{x}]$ ($x$ = 0.33), where ${\mathrm{Cu}}^{2+}$ ions form two-dimensional kagome layers. There is no magnetic order down to 50 mK, while the Curie-Weiss temperature is on the order of $\ensuremath{-}100$ K. At zero magnetic field, the low-temperature specific heat shows a ${T}^{2}$ dependence. Above 2 T, a linear temperature dependence term in specific heat emerges, and the value of $\ensuremath{\gamma}=C/T$ increases linearly with the field. Furthermore, the magnetic susceptibility tends to a constant value at $T=0$. Our results suggest that the magnetic ground state of ${\mathrm{YCu}}_{3}{(\mathrm{OH})}_{6}{\mathrm{Br}}_{2}[{\mathrm{Br}}_{1\ensuremath{-}x}{(\mathrm{OH})}_{x}]$ is consistent with a Dirac quantum-spin-liquid state with a linearly dispersing spinon strongly coupled to an emergent gauge field, which has long been theoretically proposed as a candidate ground state in the two-dimensional kagome Heisenberg antiferromagnetic system.