Spectroscopic fingerprints of a surface Mott-Hubbard insulator: the case of SiC(0001)

We discuss the spectroscopic fingerprints that a surface Mott-Hubbard insulator should show at the intra-atomic level. The test case considered is that of the Si-terminated SiC(0001)root 3 x root 3 surface, which is known experimentally to be insulating. We argue that, owing to the Mott-Hubbard phenomenon, spin unpaired electrons in the Si adatom dangling bonds are expected to,give rise to an Si 2p core level spectrum with a characteristic three-peaked structure, as seen experimentally. This structure results from the joint effect of intra-atomic exchange, spatial anisotropy, and spin-orbit coupling. Auger intensities are also discussed.