Kitaev Honeycomb Spin Liquid

Phase: B (gapless)
x-bonds (J_x σˣσˣ)
y-bonds (J_y σʸσʸ)
z-bonds (J_z σᶻσᶻ)
Majorana flux (W_p)
Kitaev (2003): Exactly solvable spin-1/2 model on honeycomb lattice. H = −Σ J_α σ_iᵅ σ_jᵅ for α-bonds.

Maps to free Majorana fermions in a static Z₂ gauge field. Phase A (gapped): one |J_α| > sum of others. Phase B (gapless): |J_α| ≤ |J_β| + |J_γ|.

Magnetic field opens gap in B phase → non-Abelian anyons (Ising model). Plaquette operators W_p = ±1 are conserved Z₂ fluxes.