Reinvestigation of the homogeneous spin model in YbMgGaO$_4$

TL;DR

This study reexamines the homogeneous spin model for YbMgGaO4 using cluster mean-field theory, revealing a field-induced phase transition and identifying parameter regimes consistent with experimental data, supporting the model's validity.

Contribution

It demonstrates that the homogeneous spin model can explain experimental observations in YbMgGaO4, including a field-induced phase transition, with specific parameter constraints.

Findings

Field-induced phase transition between stripe and 120° states.

Transition suppressed by next-nearest neighbor exchange J2/J1 > 0.13.

Theoretical spin excitation energies deviate by only 5.4% from experiments.

Abstract

Motivated by a recent inelastic neutron scattering experiment on $\mathrm{YbMgGaO}_4$ \cite{William2019}, we reinvestigate the homogeneous spin model on the triangular lattice. Using the cluster mean-field theory, we study the phase diagram and the magnetic-field-induced phase transition. We find that the phase boundary between the stripe state and the $120^{\circ}$ antiferromagnetic state is broadened by the magnetic field, leading to a field-induced phase transition. This phase transition is suppressed by the next-nearest neighbor exchange interaction $J_2/J_1$ and vanishes as $J_2/J_1>0.13$. We find a parameter space at $J_2/J_1=0.1$, in which the field-induce transition can be achieved and the deviation of theoretical spin excitation energies from experimental data is only $5.4\%$. Our results imply that an effective homogeneous spin model still works in $\mathrm{YbMgGaO}_4$.