Ultralow thermal conductivity in disordered, layered WSe₂ crystals

The cross-plane thermal conductivity of thin films of WSe₂ grown from alternating W and Se layers is as small as 0.05 watts per meter per degree kelvin at room temperature, 30 times smaller than the c-axis thermal conductivity of single-crystal WSe₂ and a factor of 6 smaller than the predicted minimum thermal conductivity for this material. We attribute the ultralow thermal conductivity of these disordered, layered crystals to the localization of lattice vibrations induced by the random stacking of two-dimensional crystalline WSe₂ sheets. Disordering of the layered structure by ion bombardment increases the thermal conductivity.