Specular Reflection Leads to Maximum Reduction in Thermal Phonon Conductivity

In contrast to established work that use diffuse surface scattering as the mechanism to lower the thermal conductivities, we show that the largest reduction of heat conduction in thin films is achieved via specular scattering. Our results create a new paradigm for heat conduction manipulation since smooth surfaces , in contrast to rough surfaces , are shown to be more effective on suppressing heat conduction.