Significant Seebeck coefficients driven by coexisting Dirac bands and van Hove singularities in bilayer Kagome borophene

Abstract

Topological semimetals typically exhibit high carrier mobility but suffer from low Seebeck coefficients due to their symmetric band structures near the Fermi level. To break this symmetry while preserving desirable transport properties, we propose engineering systems with coexisting Dirac points and van Hove singularities (VHSs). Using bilayer Kagome borophene as a prototype, first-principles calculations reveal that its Dirac cone and valence band VHS collectively create strong band asymmetry. This results in a room-temperature Seebeck coefficient of 64 μV/K at optimal doping, surpassing that of most gapless systems. Detailed electron–phonon coupling analysis indicates that the Dirac bands provide high carrier mobility, while the VHS induces a sharp peak in the density of states. Crucially, the VHS strongly enhances scattering, causing rapid variations in both relaxation time and group velocity near the singularity. These effects combine to produce an exceptionally strong energy dependence of both carrier concentration and mobility—key factors governing Seebeck coefficient enhancement. Our work establishes band asymmetry engineering via Dirac–VHS hybridization as an effective approach to enhance thermoelectric performance in semimetals.