Motivated by the recent progress in the spin-orbit-coupled triangular lattice spin liquid candidate
YbMgGaO4, we carry out a systematic projective symmetry group analysis and mean-field study of candidate
U(1) spin-liquid ground states. Due to the spin-orbital entanglement of the Yb moments, the space-group symmetry operation transforms both the position and the orientation of the local moments, and hence it brings different features for the projective realization of the lattice symmetries from the cases with spin-only moments. Among the eight
U(1) spin liquids that we find with the fermionic parton construction, only one spin-liquid state, which was proposed and analyzed by Yao Shen et al. [Nature (London) 540, 559 (2016)] and labeled as U1A00 in the present work, stands out and gives a large spinon Fermi surface and provides a consistent explanation for the spectroscopic results in
YbMgGaO4. Further connection of this spinon Fermi surface
U(1) spin liquid with
YbMgGaO4 and the future directions are discussed. Finally, our results may apply to other spin-orbit-coupled triangular lattice spin-liquid candidates, and more broadly, our general approach can be well extended to spin-orbit-coupled spin-liquid candidate materials.
For certain crystalline systems, most notably the organic compound EtMe
3Sb[Pd(dmit)
2]
2, experimental evidence has accumulated of an insulating state with a high density of gapless neutral excitations that produce Fermi-liquid-like power laws in thermodynamic quantities and thermal transport. This has been taken as evidence of a fractionalized spin-liquid state. In this Rapid Communication, we argue that if the experiments are taken at face value, the most promising spin-liquid candidates are a
Z4 spin liquid with a spinon-Fermi surface and no broken symmetries, or a
Z2 spin liquid with a spinon-Fermi surface and at least one of the following spontaneously broken: (a) time-reversal and inversion, (b) translation, or (c) certain point-group symmetries. We present a solvable model on the triangular lattice with an (a) type
Z2 spin-liquid ground state.
Triangular lattice compounds have received extensive attention recently as quantum spin liquid candidates. Here, the authors look at the
J1-
J2 Heisenberg model on the triangular lattice, and calculate the spectral function relevant for neutron scattering experiments. They find a high-energy spectrum consistent with reports of a spinon Fermi surface state in triangular lattice compounds, although the low-energy spectrum rules out such a phase, and points towards a U(1) Dirac spin liquid. They provide clear signatures to look for in future neutron scattering experiments to distinguish these two phases.