Lifetime-Broadening-Suppressed X-ray Absorption Spectrum of β-YbAlB4 Deduced from Yb 3d → 2p Resonant X-ray Emission Spectroscopy

In this work, the Yb 3d → 2p (Yb Lα1,2) resonant X-ray emission spectrum of β-YbAlB4 was acquired using excitation energies around the Yb L3-edge, at 2 K. Subsequently, the lifetime-broadening-suppressed (LBS) X-ray absorption structure (XAS) spectrum was obtained using the SIM-RIXS program. This spectrum was found to exhibit clearly resolved pre-edge and shoulder structures. Resonant Lα1 emission spectra were well reproduced from LBS-XAS profiles over wide ranges of excitation and emission energies. In contrast, noticeable discrepancies appeared between the experimental and simulated Lα2 emission spectra, suggesting an effect resulting from M4M5O1 Coster–Kronig transitions. LBS-XAS, in conjunction with partial fluorescence yield (PFY) XAS and transmission XAS, determined a value for the Yb valence (v) in β-YbAlB4 of 2.76 ± 0.08 at 2 K. Despite this relatively large uncertainty in v, each method provided a consistent variation in valence (δv) as the temperature was raised from 2 to 280 K: 0.060 ± 0.004 (L...