Determining the crystal-field ground state in rare earth Heavy Fermion materials using soft-x-ray absorption spectroscopy

TL;DR

This paper demonstrates that soft-x-ray absorption spectroscopy is an effective and versatile technique for determining the crystal-field ground state symmetry in rare earth Heavy Fermion materials, providing a complementary approach to neutron scattering.

Contribution

It introduces a theoretical mapping between polarization-dependent spectra and charge distribution of Ce 4f states, and validates the method through experimental analysis of CePd$_2$Si$_2$.

Findings

Soft-x-ray absorption spectroscopy can determine crystal-field ground states.

The method's resolution exceeds the energy scale of crystal field splitting.

Application to CePd$_2$Si$_2$ resolves previous ambiguities.

Abstract

We infer that soft-x-ray absorption spectroscopy is a versatile method for the determination of the crystal-field ground state symmetry of rare earth Heavy Fermion systems, complementing neutron scattering. Using realistic and universal parameters, we provide a theoretical mapping between the polarization dependence of Ce $M_{4,5}$ spectra and the charge distribution of the Ce $4f$ states. The experimental resolution can be orders of magnitude larger than the $4f$ crystal field splitting itself. To demonstrate the experimental feasibility of the method, we investigated CePd$_2$Si$_2$, thereby settling an existing disagreement about its crystal-field ground state.