CONSTRUCTIVE ROLE OF ANHARMONICITY IN THERMAL-CONDUCTIVITY

It is shown that the Peierls vector integral of motion can be extended such that it applies also to anharmonic phonon systems, provided they remain translationally invariant. This hints at the possibility of ba llistic transport. In the classical regime it is in agreement with the existence of propagating solitons in the Toda and the Fermi-Pasta-Ula m chains. For quantal energy transport it provides new aspects for the concept of Umklapp scattering and, as regards energy transport in dis ordered materials, for speculations about a possible constructive role of anharmonicity.