Polaronic anharmonicity in the Holstein-Hubbard model

Abstract
We demonstrate for the nearly half-filled Holstein-Hubbard model that the presence of antiferomagnetic spin correlations can cause polaronic carrier self-localization, and hence a strongly anharmonic lattice potential, already at moderate electron-phonon coupling strengths λ∼0.2–0.4, up to substantial hole dopant concentrations ch∼(20–30)%. The results are compared to recent observations of anharmonicity in the apical oxygen c-axis motion of cuprate superconductors.