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

2D beryllium polynitrides or beryllonitrene is a newly synthesized layered material displaying anisotropic Dirac cones and van Hove singularity (VHS) located only approximate to 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 (kappa(ph)) of 78.6 and 98.8 W mK(-1), and an electron thermal conductivity (kappa(e)) of 23.0 and 60.7 W mK(-1), along the in-plane directions. kappa(ph) 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 kappa(ph) by up to 55%. Instead, kappa(e) 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 kappa(e) upon filling of the Dirac cones until VHS.

Automated summary

The study reveals that beryllonitrene, a newly synthesized layered material, exhibits anisotropic thermal and electrical transport properties. The in-plane phonon thermal conductivity is dominated by flexural acoustic modes, while the electron thermal conductivity shows nonmonotonic variations with carrier density.