Significant Increase of Electron Thermal Conductivity in Dirac Semimetal Beryllonitrene by Doping Beyond Van Hove Singularity

Abstract

2D beryllium polynitrides or beryllonitrene is a newly synthesized layered material displaying anisotropic Dirac cones and van Hove singularity (VHS) located only ≈0.5 eV above the Fermi level. Using the Boltzmann transport equation with many-body effects and first-principles calculations, it is uncovered that beryllonitrene has an in-plane anisotropic room-temperature phonon thermal conductivity (κph) of 78.6 and 98.8 W mK−1, and an electron thermal conductivity (κe) of 23.0 and 60.7 W mK−1, along the in-plane directions. κph is dominated by the large heat capacity flexural acoustic (ZA) modes, which are susceptible to three-phonon and four-phonon scatterings but rather immune to scattering onto electrons. Filling the Dirac cones till VHS and above gradually enhances the phonon–electron coupling and monotonically decreases κph by up to 55%. Instead, κe displays unusual nonmonotonic variations with the increase in the carrier density and follows the electron density of states at corresponding Fermi levels. The results shed light on the thermal and electrical transport properties in beryllonitrene and reveal a thermal conductivity modulation mechanism that includes a 60% increase of κe upon filling of the Dirac cones until VHS.Theoretical models that consider all possible carrier scattering mechanisms using density functional theory, find a significant impact of n-doping on the electron thermal transport after reaching the van Hove singularity point in beryllonitrene. This finding suggests a new way to tune the electron thermal conductivity of 2D materials, including graphene.