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Title: Nature of the spin liquid in the triangular $J1-J2$ Heisenberg model
Plain: Adding a weak second-neighbor coupling to the triangular-lattice Heisenberg model destroys its 120-degree magnetic order and produces a nonmagnetic phase. Whether this phase is a gapless Dirac spin liquid, a gapped spin liquid or a chiral state is unsettled.
Precise: Model: H = J1 sum_<ij> S_i . S_j + J2 sum_<<ij>> S_i . S_j, $S = 1/2$, triangular lattice, roughly $0.07 < J2/J1 < 0.15$. Determine the phase ($U(1)$ Dirac spin liquid, $Z2$ spin liquid, chiral spin liquid or valence-bond order) and its boundaries. An answer gives the classification with spin and singlet gaps extrapolated to infinite size.
Settled by: Agreement of several unbiased methods (DMRG with flux insertion, PEPS, neural-network states) on extrapolated gaps and on the monopole and spinon spectrum.
Kind: well-posed
Answer type: classification
References: (empty)
Literature status: contested
Status note: DMRG with flux insertion (Hu et al., PRL 2019) supports a Dirac spin liquid; other variational and tensor-network studies report gapped or ordered states.
Posed since: (empty)