Co-existence of size-dependent and size-independent thermal conductivities in single layer black phosphorus

TL;DR

This study combines computational methods to reveal that single layer black phosphorus exhibits both size-dependent and size-independent thermal conductivities along different crystallographic directions, highlighting its anisotropic heat transport properties.

Contribution

It uncovers the coexistence of size-dependent and size-independent thermal conductivities in single layer black phosphorus, a phenomenon not observed in similar 2D materials.

Findings

Thermal conductivity along ZZ direction is size-dependent.

Thermal conductivity along AM direction is size-independent.

Significant anisotropy in thermal conductivities at 300 K.

Abstract

Thermal conductivity of single layer black phosphorus (BP) is investigated by combining density functional calculations and Peierls-Boltzmann transport equation. Differing from isotropic and divergent thermal conductivities in two-dimensional graphene and MoS$_2$, an compelling co-existence of size-dependent and size-independent thermal conductivities are discovered for single layer BP along zigzag (ZZ) and armchair (AM) direction, respectively. Besides, thermal conductivities in single layer BP are found to be highly anisotropic because of orientation dependent group velocities, e.g., thermal conductivities at 300 K are 83.5 and 24.3 W/m-K along ZZ and AM directions for single layer BP with a size of 10 $\mu m$, respectively.