QUANTUM-WELL STATES IN METALLIC THIN-LAYERS

When going from the bulk solid to a thin-film of nanometer dimensions, the electronic structure becomes discretized in the perpendicular dir ection. These discrete states, also called thin film states and quantu m well states, are clearly distinguished in photoemission experiments as two-dimensional and thickness-dependent modulations of the bulk spe ctra, although their observation is limited to highly perfect epitaxia l systems. The photoemission data are well explained in the framework of a simple model for the electron wave function in a quantum well sta te. Thin film states become spin-polarized when growing on ferromagnet ic substrates. Furthermore, spin-polarized, thickness-dependent modula tions at a given energy lead to spin-dependent periodic oscillations o f the density of states as a function of thickness, which are found to be responsible for the oscillatory coupling observed in magnetic mult ilayers.