SiC(0001): A surface Mott-Hubbard insulator

Abstract

We present ab initio electronic structure calculations for the Si-terminated SiC(0001)$\sqrt{3}\ifmmode\times\else\texttimes\fi{}\sqrt{3}$ surface. While local-density approximation (LDA) calculations predict a metallic ground state with a half-filled narrow band, Coulomb effects, included by the spin-polarized LDA+U method, result in a magnetic (Mott-Hubbard) insulator with a gap of $1.5$ eV, comparable with the experimental value of $2.0$ eV. The calculated value of the intersite exchange parameter, $J=30$ K, leads to the prediction of a paramagnetic Mott state, except at very low temperatures. The observed Si 2p surface core-level doublet can naturally be explained as an on-site exchange splitting.