Dispersion of quantum well states in Cu/Co/Cu(001)

Quantum well states (QWS's) in Cu thin films grown on Co/Cu(001) were studied using angle-resolved photoemission spectroscopy. For the normal photoemission, QWS's from both lower and higher energy bands relative to the vacuum level were measured, and explained by phase accumulation method. QWS's from the lower band were studied in detail as a function of the in-plane momentum k_∥. We found that the QWS dispersion depends on the Cu film thickness. From the experimental data, we deduced the quantized perpendicular momentum k_⊥ and the energy as a function of k_∥. Our results show that the in-plane effective mass can not be obtained by a simple parabolic fitting of the E vs k_∥ due to the dependence of k_⊥ on k_∥.