  By way of the nonequilibrium Green's function simulations and first
principles calculations, we report that borophene, a single layer of boron
atoms that was fabricated recently, possesses an extraordinarily high lattice
thermal conductance in the ballistic transport regime, which even exceeds
graphene. In addition to the obvious reasons of light mass and strong bonding
of boron atoms, the superior thermal conductance is mainly rooted in its strong
structural anisotropy and unusual phonon transmission. For low-frequency
phonons, the phonon transmission within borophene is nearly isotropic, similar
to that of graphene. For high frequency phonons, however, the transmission is
one dimensional, that is, all the phonons travel in one direction, giving rise
to its ultrahigh thermal conductance. The present study suggests that borophene
is promising for applications in efficient heat dissipation and thermal
management, and also an ideal material for revealing fundamentals of
dimensionality effect on phonon transport in ballistic regime.
