HOPPING THEORY OF HEAT-TRANSPORT IN DISORDERED-SYSTEMS

Heat transport is studied in a simple model system of Anderson localiz ed optical (carrier) phonons which perform thermally activated hopping due to anharmonic interaction with delocalized acoustic phonons. The corresponding kinetic equations (rate equations) are derived by using the density-matrix formalism. The calculated hopping contribution to t he heat conductivity exhibits a linear increase with temperature at lo wer temperatures and (depending on the choice of parameters) eventuall y reaches a ''saturated'' value at higher temperatures. Thus, unlike o ther authors, we do not need a special mechanism, such as lifetime bro adening of the optical phonon states, to explain the transition to the saturation region. Furthermore, we show that particle (carrier) numbe r nonconservation leads to a quenching of the hopping mechanism.