Kondo scale and coupled fluorescence across the γ−α transition in Ce0.93Sc0.07

We present a resonant inelastic x-ray scattering (RIXS) study across the $\mathrm{temperature}\phantom{\rule{0.16em}{0ex}}(T$) driven $\ensuremath{\gamma}\text{\ensuremath{-}}\ensuremath{\alpha}$ transition in ${\mathrm{Ce}}_{0.93}{\mathrm{Sc}}_{0.07}$. RIXS measurements across the Ce ${\mathrm{M}}_{5}$ edge unambiguously identify the ${f}^{1}\phantom{\rule{4pt}{0ex}}\ensuremath{\rightarrow}\phantom{\rule{4pt}{0ex}}{f}^{0}$ and ${f}^{1}\phantom{\rule{4pt}{0ex}}\ensuremath{\rightarrow}\phantom{\rule{4pt}{0ex}}{f}^{2}$ charge excitations, which provide a quantification of the Ce on-site Coulomb repulsion energy, ${U}_{ff}$. Calculation with a simplified single-impurity Anderson model combined with full multiplet theory reproduces the charge excitations and establishes that the very different Kondo temperatures of the $\ensuremath{\gamma}$ to $\ensuremath{\alpha}$ phase are reflected in RIXS spectra. A systematic $T$-dependent hysteresis is observed for the ${f}^{0}$ final state spectral intensity upon cycling across the $\ensuremath{\gamma}\text{\ensuremath{-}}\ensuremath{\alpha}$ transition. In addition, a fluorescencelike structure also follows the same hysteretic behavior and shows it is directly connected to the weight of the ${f}^{0}$ configuration in the ground state. The results indicate that the Ce M-edge RIXS is a reliable quantitative probe of the electronic structure of strongly correlated Ce-based Kondo systems and is sensitive to the emergent Kondo energy scale.