Coexisting electronic correlations and electron-phonon interactions have been proposed to lead to dynamic polaron-tunneling behavior for the axial oxygen in ${\mathrm{YBa}}_2$${\mathrm{Cu}}_3$${\mathrm{O}}_7$. Emphasizing nonlinear and nonadiabatic effects, we show that this description leads to distinctive predictions consistent with structural, optical, and inelastic neutron-scattering data in the axial direction.

• Received 12 October 1993

DOI:https://doi.org/10.1103/PhysRevB.49.3671