Quantum-well states in Cu/Co overlayers and sandwiches

We report ab initio calculations of quantum-well states in Cu/Co(001) and Co/Cu(001) overlayers and in Co/Cu/Co(001) sandwiches. Overlayer states are found which coincide well with those previously identified in photoemission and inverse photoemission experiments. In Cu/Co and at energies overlapping with the substrate continuum, minority spin resonances are clearly identifiable. However, in the majority spin channel coupling to the substrate is strong enough to effectively destroy quantum-well features. In Co/Cu/Co(001) sandwiches discrete states are found at similar energies to those in overlayers of corresponding Cu thicknesses, but well defined resonance states are absent in both spin channels. There is no longer a strongly size-dependent electronic structure at the Fermi energy. We conclude care must be taken in extrapolating from the electronic structure of overlayer systems to that of other modulated structures.