Magnetic Frustration — Triangular Lattice

Antiferromagnetic Ising spins on a triangular lattice. No ground state can satisfy all bonds simultaneously — geometric frustration produces extensive degeneracy.

Temperature T = 0.50
J (coupling)
E = —
AFM on triangular lattice: each triangle has 3 bonds; at least one must be "frustrated" (parallel spins for J<0). Ground state degeneracy ∝ exp(N·s) with s=0.323/site — extensive entropy at T=0 → spin liquid behavior. Contrast FM: J>0 has unique ordered ground state, no frustration.