Study of crystal-field splitting in ultrathin CePt5 films by Raman spectroscopy

The low-temperature electronic properties of rare-earth intermetallics are substantially influenced by the symmetry and magnitude of the crystal electric field. The direct spectroscopic analysis of crystal-field splitting can be challenging, especially in low-dimensional systems, because it requires both high spectral resolution and pronounced sensitivity. We demonstrate the eligibility of electronic Raman spectroscopy for this purpose by the direct determination of the 4f level splitting in ultrathin ordered CePt5 films down to approximate to 1.5 nm thickness on Pt(111). Crystal-field excitations of Ce 4f electrons give rise to Raman peaks at energy losses up to approximate to 25 meV. Three distinct peaks occur which we attribute to inequivalent Ce sites, located (i) at the interface to the substrate, (ii) next to the Pt-terminated film surface, and (iii) in the CePt5 layers in between. The well-resolved Raman signatures allow us to identify a reduced crystal-field splitting at the interface and an enhancement at the surface, highlighting its strong dependence on the local atomic environment.