Unoccupied surface state on the (root 3x root 3) R30 degrees reconstruction of 6H-SiC(0001)

Applying k-resolved inverse photoemission (KRIPES) to the root 3 x root 3 R30 degrees-reconstructed 6H-SiC(0001) face, we have observed a sharp surface state U located at 1.10 +/- 0.05 eV above the Fermi level at the centre of the surface Brillouin zone. Its bandwidth of 0.34 +/- 0.05 eV is in good agreement with the 0.35 eV predicted by first-principle calculations based on a Si-adatom model. However, LDA calculations predict a half-filled Sigma(1) state and a metallic character for this reconstruction. Together with recent ARUPS data, our results reveal that the one-electron band Sigma(1) is split into two bands, giving a semiconducting surface with a reduced indirect bandgap around 2.0 eV at the <(K)' over bar> point. Many-body correlation effects may give rise, in the limit of strong localization, to this bandgap opening.