Gapless quantum spin liquid ground state in the two-dimensional spin-1/2 triangular antiferromagnet YbMgGaO4.

Yuesheng Li,Zhonghua Wu,Junfeng Wang,Langsheng Ling,Li Pi,Youming Zou,Shiyan Li,Zhaorong Yang,Feng Jin,Zhen Zhang,Qingming Zhang,Lei Zhang,Haijun Liao

doi:10.1038/srep16419

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 YbMgGaO4 with 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 θw ~ −4 K), the power-law temperature dependence of heat capacity and nonzero susceptibility at low temperatures suggest that YbMgGaO4 is a promising gapless (≤|θw|/100) QSL candidate. The residual spin entropy, which is accurately determined with a non-magnetic reference LuMgGaO4, 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.

Highlights

Systems and are difficult to determine precisely
We report the successful synthesis of a new triangular antiferromagnet with effective spin-1/2, YbMgGaO4
The new compound overcomes some critical disadvantages in the existing materials, such as spatially anisotropic intralayer exchange interactions, magnetic defects, interlayer exchange coupling, and antisymmetric DM interactions

Summary

Introduction

Systems and are difficult to determine precisely. The complications caused by these factors make extraction of the intrinsic physics from real systems difficult. The aforementioned structural disadvantages are avoided in the new compound. It has spatially isotropic and perfect triangular layers with R3m symmetry. The nonmagnetic reference compound LuMgGaO4 is available for control experiments, such as precisely excluding the lattice heat capacities for YbMgGaO4. No magnetic ordering is observed at least down to 60 mK from both magnetization and heat capacity measurements, despite the obvious AF exchange interaction between nearest-neighbor spins (θ w ~ − 4 K) suggesting that YbMgGaO4 is a new QSL candidate. The power-law temperature dependence of heat capacity and nonzero susceptibility further indicate that the excitation gap from the GS should be no more than ~ |θ w|/100 at low temperatures[17,18]. An anomalous susceptibility plateau is first observed at paramagnetic states (0.5 K), which imply an unusual field-induced quantum spin state

Methods

Results

Conclusion