Controlled electronic coupling between two quantum wells: A photoemission study of noble-metal systems

Double quantum wells are grown on Au(111) and Cu(111) substrates using Ag as the well material and either Cu or Au as a barrier material. The barrier thickness is varied to change the coupling between the two wells, and the resulting double-quantum-well states are probed with photoemission. In the limit of a very thick barrier, the coupling is eliminated, and the allowed states become those of two independent wells. When the barrier thickness is reduced to zero, the two quantum wells combine to form a single well. Between these two limits, the observed evolution of the binding energies and intensities is compared with the predictions of a simple theoretical model based upon Bloch wave functions. The effects of smoothing the barrier potential are studied by annealing a Au barrier sample, allowing atomic interdiffusion between the Au barrier and the Ag wells.