Study of crystal-field splitting in ultrathin CePt$_5$ layers by Raman spectroscopy

TL;DR

This study demonstrates that electronic Raman spectroscopy can effectively measure crystal field splitting in ultrathin CePt$_5$ layers, revealing how local atomic environments influence electronic properties at the nanoscale.

Contribution

It introduces Raman spectroscopy as a direct method to analyze crystal field splitting in low-dimensional rare-earth intermetallics, providing spatially resolved insights.

Findings

Raman peaks indicate crystal field excitations up to 25 meV.

Distinct peaks correspond to different Ce sites within the layers.

Crystal field splitting varies with local atomic environment, decreasing at the interface and increasing at the surface.

Abstract

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 ultra-thin ordered CePt$_5$ films down to 1.7 nm thickness on Pt(111). Crystal field excitations of Ce $4f$ electrons give rise to Raman peaks with energy shifts up to $\approx$ 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 surface, and (iii) in the CePt$_5$ 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.