Electrostatic screening

Mobile electric charges redistribute in response to an imposed electric potential, partly compensating its field. The induced density response and the Poisson equation must be solved self-consistently. Classical dilute mobile ions lead to the Debye–Hückel approximation; a degenerate electron system instead has a response set by its electronic compressibility and interactions. A high charge response can pin a partly occupied Landau level near the Fermi energy, whereas an incompressible gap suppresses that response. electrostatic screening is not a claim that every material perfectly excludes every static field.