ANHARMONIC EXCITATIONS IN HIGH T-C MATERIALS

Some chains of atoms in YBa2Cu3O7, Y2Ba4Cu6O13 and La2CuO4 behave as q uasi-one-dimensional structures in which anharmonic self-focusing brea thers can propagate. Such breathers have no threshold energy and are c reated in response to perturbations of the lattice by charge movement and in charge self-trapping. The creation and directionally selective propagation of such breathers occurs whatever the charge pairing mecha nism. The presence of quasi-one-dimensional chains appears to be a nec essary structural condition for high T-c behaviour in the layered fami ly based on (Ni2B2).