Edwards-Anderson spin glass on a 2D lattice with random ±J couplings. At low T, spins freeze into a disordered but stable configuration — a spin glass phase with broken replica symmetry.
H = −Σ Jᵢⱼ σᵢσⱼ | Jᵢⱼ ~ ±J + disorder | T_sg ≈ J/k_B (EA transition)