Reduction of thermal conductivity of anharmonic lattices

We study how to reduce thermal conductivity of anharmonic lattices. It is shown that high density of interface is an efficient way to get ultralow thermal conductivity, however, it does not work well when the density exceeds a certain value. This behavior is even clearer in harmonic lattices. The saturation of thermal conductivity in the case of disordered interface is similar to recent experiment results by Costescu in disordered multilayers of W/Al2O3 [Science 303, 989 (2004)].