A one-dimensional model Hamiltonian is considered, representative, for example, of a displacive unstable lattice ferroelectric. Krumhansl and Schrieffer have shown previously that domain-wall displacement patterns arise in a classical analysis, as a consequence of inherent nonlinearity. Using a simple variational method, a quantum description of these walls (both stationary and moving) is given, and it is shown that their appearance as elementary excitations in the system survives the passage from classical to quantum mechanics.

• Received 29 March 1976

DOI:https://doi.org/10.1103/PhysRevB.14.2966