Nature of the intermediate phase of the antiferromagnetic Kitaev model in a field
In plain words
Numerical studies of the ideal antiferromagnetic Kitaev model in a field along the cube diagonal find an extra phase between the low-field spin liquid and the high-field polarized state. Its identity, possibly a gapless spin liquid with a Fermi surface of neutral particles, is disputed.
Precise statement
Model: H = K sum_<ij>_gamma S^gamma_i S^gamma_j - h sum_i (S^x_i + S^y_i + S^z_i)/sqrt(3), $K > 0$, $S = 1/2$, honeycomb lattice. For the window h_c1 < h < h_c2 found numerically, determine whether the ground state is a gapless $U(1)$ spin liquid with a spinon Fermi surface, a gapped chiral spin liquid of different Chern number, or another phase. An answer gives the classification, its boundaries in $h/K$, and the supporting entanglement and spectral evidence.
What would settle it
Large-cylinder DMRG, iPEPS or neural-network variational calculations that agree on the gap, entanglement scaling and topological invariants of the intermediate phase.