Gapless quantum spin liquid ground state in the two-dimensional spin-1/2 triangular antiferromagnet YbMgGaO$_4$

摘要: Quantum spin liquid (QSL) is a novel state of matter which refuses the conventional freezing even at 0 K. Experimentally searching for structurally perfect candidates big challenge in condensed physics. Here we report successful synthesis new spin-1/2 triangular antiferromagnet YbMgGaO$_4$ with R$\bar{3}$m symmetry. The compound an ideal two-dimensional and spatial isotropic magnetic triangular-lattice has no site-mixing defects antisymmetric Dzyaloshinsky-Moriya (DM) interactions. No down to 60 mK (despite $\Theta$$_w$ $\sim$ -4 K), low-T power-law temperature dependence heat capacity nonzero susceptibility suggest that promising gapless ($\leq$ $|$$\Theta$$_w$$|$/100) QSL candidate. residual entropy, accurately determined non-magnetic reference LuMgGaO$_4$, approaches zero ($<$ 0.6 \%). This indicates possible ground (GS) frustrated system been experimentally achieved lowest measurement temperatures.