Signature of surface periodicity in the electronic structure of Si (111)-(7x7)

The surface electronic structure of Si(1 1 1)-$7\times 7$ has been studied by angle-resolved photo electron spectroscopy. Replicas of the S 1 surface state are found in correspondence with several $7\times 7$ unit cells in the reciprocal space. This observation resolves in a direct way the long-standing dichotomy between the structural and electronic properties of the system previously discussed on the basis of the $2\times 2$ or $\sqrt{3}\times \sqrt{3}$ R30° surface models.