Survival of the Kitaev spin-liquid region at larger spin

Determine whether the narrow quantum spin-liquid region of the spin-$S$ Kitaev-Heisenberg model survives for spin lengths larger than those examined, while accounting for the dependence on the choice of Schwinger-boson mean-field saddle point.

Background

The paper finds that the quantum spin-liquid regions around the ferromagnetic and antiferromagnetic Kitaev points shrink rapidly as the spin length increases, becoming very narrow at $S=2$. The phase boundaries are obtained from instabilities of a fixed Schwinger-boson mean-field saddle point treated with perturbative RPA.

The authors note that the fate of this trend at larger spin may depend on which Schwinger-boson mean-field saddle point is used. Thus, establishing whether a quantum spin-liquid region persists beyond the studied spin values requires extending the analysis to larger $S$ and assessing the dependence on competing saddle points.