Correlation effects and spin-orbit interactions in two-dimensional hexagonal 5d transition metal carbides, Ta^sub n+1^C^sub n^ (n = 1, 2, 3)

Density functional calculations are used to investigate the electronic structure of two-dimensional 5d tantalum carbides with honeycomb-like lattice structures. The authors focus on changes in the low-energy bands near the Fermi level with dimensionality. They find that the Ta 5d states dominate, and the extended nature of the wave functions makes them weakly correlated. The carbide sheets are prone to long-range magnetic order. The authors evaluate its stability to enhanced electron-electron interactions through a Hubbard U correction. Lastly, they find that the splitting of the bands near the Fermi level caused by spin-orbit interaction decreases with increasing dimensionality. In the lowest-dimensionality case, the band splitting pushes a conduction band above the Fermi level and leads to a semi-metallic state.