Partially occupied surface state at the Fermi level of La(0001)

A partially occupied surface state at the Fermi level of a well-ordered La(0001) film grown on W(110) is observed by photoemission and inverse photoemission, which provide direct pictures of the occupied and unoccupied part, respectively. The occupied part of the surface state gives rise to an intense direct recombination line in the N_4,5O_2,3O_2,3 Auger-electron spectrum. The surface state is found to be sensitive to O₂ adsorption and disordering of the surface induced by Ar-ion bombardment. The present results support a view that such surface states occur generally on close-packed surfaces of the rare-earth metals.