Thermal Conductance Boost in Phononic Crystal Nanostructures

A theoretical study of coherent phonon scattering in thin-film phononic-crystal nanostructures (also called thermocrystals) is presented. It is commonly assumed that phononic crystals may only reduce thermal conductivity of materials. In this theoretical paper, contrary to this assumption, we demonstrate that phononic nanopatterning can enhance the thermal conductance of thin films under certain conditions. That is to say, it is shown that a thin membrane with many holes can have a higher thermal conductance than an unpatterned membrane. This effect originates from the increase in the density of states due to the coherent modifications of phonon dispersion. This counterintuitive phenomenon, called the thermal conductance boost effect, can be used for applications involving phonon management.