Effective models

Throwing away what does not matter at low energy — the art of writing the simplest model that still contains the physics.

Every topic that illustrates this idea, drawn from across all subjects.

• Strong Coupling: Perturbation Theory and Superexchange Mott Physics in Correlated Lattices In the opposite limit U ≫ t, treating hopping as a perturbation and projecting out doubly occupied sites with a Schrieffer–Wolff transformation maps the half-filled Hubbard model onto the antiferromagnetic Heisenberg model, with superexchange J = 4t²/U.