Giant thermal conductivity in diamane and the influence of horizontal reflection symmetry on phonon scattering.

Diamane, a chemically derived two-dimensional material, shows many superior physical and chemical properties similar to diamond thin films. Through the Peierls-Boltzmann transport equation, we reveal giant thermal conductivity in diamane with a stacking order of both AB and AA (respectively, abbreviated as D-AB and D-AA, hereafter) which are both comparable to that of diamond. Like in graphene, the phonon transport falls into the hydrodynamic regime even at room temperature, and the major contribution to the total thermal conductivity comes from the out-of-plane acoustic phonon modes (>40%). In addition, the thermal conductivity shows a dependence on the stacking order, namely, the thermal conductivity of D-AA, ∼2240 W m-1 K-1 at 300 K, is around 15% larger than that of D-AB, which is due to the strong restriction on the phonon scattering phase space induced by the horizontal reflection symmetry in D-AA. Such a kind of restriction, not limited to single atomic plane systems, is a general feature in two-dimensional materials with a horizontal reflection symmetry.