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

TL;DR

This study reports the synthesis and characterization of YbMgGaO$_4$, a structurally perfect two-dimensional spin-1/2 triangular antiferromagnet, which exhibits properties consistent with a gapless quantum spin liquid ground state down to very low temperatures.

Contribution

The paper presents the first experimental realization of a gapless quantum spin liquid in a structurally perfect, defect-free YbMgGaO$_4$ compound with no spin freezing down to 60 mK.

Findings

No spin freezing observed down to 60 mK

Heat capacity follows a low-temperature power-law behavior

Residual spin entropy approaches zero (<0.6%)

Abstract

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