YbMgGaO₄: A Triangular‐Lattice Quantum Spin Liquid Candidate

Abstract

Resonating valence bond ground state, the prototype of a quantum spin liquid (QSL), had been first proposed by P. W. Anderson back in 1973 on the triangular lattice. In such a 2D QSL, spinons created as unpaired spins can propagate by locally rearranging the uncorrelated valence bonds. However, the corresponding candidate materials are still rare to date. YbMgGaO4, first proposed in 2015 may fill this gap: the magnetic rare‐earth Yb3+ ions arrange on the triangular lattice with the perfect R‐3m symmetries and with a large interlayer distance. No conventional spin freezing is observed down to 40 mK without residual magnetic entropy, despite the significant antiferromagnetic coupling of ≈2 K. This report reviews and classifies the relevant experimental and theoretical progress on some (effective) spin‐1/2 triangular antiferromagnets, especially on YbMgGaO4, followed by discussion and outlook on some of the pending issues.

Yb delafossites: unique exchange frustration of 4f spin 1/2 moments on a perfect triangular lattice

“…However, it is not possible to estimate these off diagonal contributions on the basis of the available data. This is not unusual and is also true for the other prominent Yb 3+ triangular lattice system YbGaMgO 4 [53,79].…”

“…It must also be noted that the effective exchange constants J and J ⊥ in the NaYbCh 2 materials are comparatively large for an Yb 3+ triangular lattice. In YbMgGaO 4 , NaBaYb(BO 3 ) 2 and Rb 3 Yb(PO 4 ) 2 the lowtemperature Curie-Weiss temperatures and thus the exchange constants are more than one order of magnitude smaller compared to the NaYbCh 2 system [53,[79][80][81]. In this sense, these other systems with small exchange couplings can be regarded as nearly-single-ion systems (without significant exchange coupling between the ions).…”

Synthesis and Anisotropic Magnetism in Quantum Spin Liquid Candidates $A$YbSe$_2$ ($A$ = K and Rb)

“…[13][14][15][16][17][18][19] One Yb 3+ based triangular lattice material, YbMgGaO 4 , has been proposed as a QSL candidate by the magnetization, heat capacity, neutron scattering, muon spin relaxation and thermal conductivity measurements. [20][21][22][23][24][25][26][27][28] YbMgGaO 4 crystallizes in high symmetry (trigonal R-3m) by creating a perfect Yb 3+ triangular magnetic lattice. Non-magnetic Mg 2+ and Ga 3+ ions separate the Yb 3+ triangular magnetic layers by 8.4 Å and the distance between the two Yb 3+ ions within the layer is 3.4 Å, which provides well 2D character for YbMgGaO 4 .…”

Magnetic properties and signatures of moment ordering in triangular lattice antiferromagnet KCeO$_2$

“…While the triangular lattice is a relatively common lattice motif, few materials show signatures of hosting intrinsically quantum disordered magnetic ground states. Recently, several rare earth, Yb-based oxides were reported to form quantum disordered ground states, with prominent examples being YbMgGaO 4 [16][17][18][19][20][21][22][23][24][25][26][27] and NaYbX 2 (X = chalcogenide) [11,[28][29][30][31][32][33][34][35][36]. These and related materials do not form longrange magnetic order and instead display continuum spin excitations and thermodynamic properties consistent with QSL ground states.…”