Coexistence of size-dependent and size-independent thermal conductivities in phosphorene

Thermal conductivity of single layer phosphorene is investigated by combining density functional calculations and the Peierls-Boltzmann transport equation. Differing from isotropic and divergent thermal conductivities in two-dimensional graphene and MoS2, a compelling coexistence of size-dependent and size-independent thermal conductivities is discovered for single layer black phosphorus (BP) along zigzag (ZZ) and armchair (AM) directions, respectively. Additionally, thermal conductivities in single layer phosphorene are found to be highly anisotropic because of orientation dependent group velocities and phonon relaxation times; e.g., thermal conductivities at 300 K are 83.5 and 24.3 W/m K along ZZ and AM directions, respectively, for single layer BP with a size of 10 mu m.