Large spin-orbit splitting in light quantum films: Al/W(110)

We investigate the long-standing question whether or not a large spin-orbit splitting can be induced in a light quantum film by a substrate effect. It is shown that quantum-well states in Al films on W(110) display large Rashba-type spin-orbit splittings up to at least ten monatomic layers (MLs) in angle-resolved photoemission measurements with and without spin resolution. Moreover, at 10 ML thickness, a non-Rashba-type behavior of the splitting is observed attaining its maximum value (Delta(so) similar to 0.3 eV) for electron wave vectors around the border of the projected substrate band gap. This deviation from the Rashba model is explained as direct interaction of quantum-well states with spin-orbit split states of the substrate.