Frustrated magnets on the kagome lattice — resonating valence bonds, no long-range order, fractionalized excitations
H = J₁ Σ⟨i,j⟩ Sᵢ·Sⱼ + J₂ Σ⟪i,j⟫ Sᵢ·Sⱼ (frustrated Heisenberg)
RVB state: |ψ⟩ = Σ_configs c_p |dimer covering⟩ (Anderson 1973)
Wilson loop: W = ⟨∏ σᵢᶻ⟩ detects Z₂ topological order
Spinon: fractionalized S=½ excitation — no magnon, no coherent quasiparticle