Kagome flat band interaction in Ce 4f resonant photoemission of pyrochlore CeRu₂

A strong 0.5 eV Ce 4f satellite peak in the Ce 3d-edge resonant photoemission (ResPES) of CeRu₂ (in comparison to CeRu₂Si₂) helped launched the field of bulk-sensitive soft x-ray and hard x-ray photoemission [1]. Recently, a 0.5 eV density of states peak in non-resonant valence band photoemission of CeRu₂ has been clarified to originate from the Kagome-like Ru-d flat bands in the pyrochlore crystal structure [2]. Here a fine excitation energy-step mapping of the Ce 3d-4f ResPES process reveals that the 0.5 eV resonant enhancement of 4f weight distinctly occurs past the absorption threshold and the Fermi-level 4f resonant enhancement, and is interpreted as a strong interatomic resonant Auger effect enabled by the strong hybridization mixing and fast timescale hopping interaction between the two narrow bandwidth Ce 4f and Ru 4d states. This behavior is contrasted to the ResPES and Auger emission of related CeFe₂.

[1] A. Sekiyama et al., Nature 403, 396 (2000).

[2] J. Huang et al., npj Quantum Mater. 9, 71 ( 2024).