Spin dependent avoided crossing effect on quantum well states in Al W 110

Despite their low atomic number, Al films show large spin orbit splittings when grown on W 110 . Our spin and angle resolved photoemission experiment reveals two types of spin orbit split states quantum well states QWSs with small Rashba splitting proportional to the electron wave vector in the film plane k [Rashba parameter amp; 945;R amp; 8764; 7 10 amp; 8722;12 eVm for a 10 monolayer ML film] and substrate derived interface states with large amp; 8764;0.5 eV splitting. The E k dispersion of this pair of interface states changes only slightly up to 3 ML Al. At higher Al coverages, the QWSs and interface states show a remarkable avoided crossing effect in their band dispersions. This avoided crossing effect obeys symmetry as well as spin and, therefore, leads to a strongly enhanced spin orbit splitting of Al QWSs. This is shown by E k band dispersions and by spin and angle resolved spectra for several thicknesses up to 15 ML A