Electronic stopping of slow protons in transition and rare earth metals: Breakdown of the free electron gas concept

The electronic stopping cross sections (SCS) of Ta and Gd for slow protons have been investigated experimentally. The data are compared to the results for Pt and Au to learn how electronic stopping in transition and rare earth metals correlates with features of the electronic band structures. The extraordinarily high SCS observed for protons in Ta and Gd cannot be understood in terms of a free electron gas model, but are related to the high densities of both occupied and unoccupied electronic states in these metals.Financial support of this work by the Austrian Science Fund (FWF-Project No. P22587-N20 and FWFProject No. P25704-N20) is gratefully acknowledged. M. V. M. acknowledges financial support from São Paulo/Brazil funding agency FAPESP under Contract No. FAPESP2013/09105-0. A research infrastructure fellowship of the Swedish Foundation for Strategic Research (SSF) under Contract No. RIF14-0053 supporting accelerator operation is acknowledged.Peer Reviewe