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><…

We studied the magnetic properties of YCu$_3$(OH)$_6$Br$_2$[Br$_{1-x}$(OH)$_{x}$] ($x$ = 0.33), where Cu$^{2+}$ ions form two-dimensional kagome layers. There is no order down to 50 mK while Curie-Weiss temperature on -100 K. At zero field, low-temperature specific heat shows a $T^2$ dependence. Above 2 T, linear dependence term in emerges, and value $\gamma C/T$ increases linearly with field. Furthermore, susceptibility tends constant at $T 0$. Our results suggest that ground state consistent Dirac quantum-spin-liquid dispersing spinon strongly coupled an emergent gauge which has long been theoretically proposed as candidate Heisenberg antiferromagnetic system.