Electronic structure and 4 f -electron character in Ce 2 PdIn 8 studied by angle-resolved photoemission spectroscopy

The localized-to-itinerant transition of $f$ electrons lies at the heart of heavy-fermion physics, but has only been directly observed in single-layer Ce-based materials. Here, we report a comprehensive study on the electronic structure and nature of the Ce $4f$ electrons in the heavy-fermion superconductor ${\mathrm{Ce}}_{2}{\mathrm{PdIn}}_{8}$, a typical $n=2 {\mathrm{Ce}}_{n}{\mathrm{M}}_{m}{\mathrm{In}}_{3n+2m}$ compound, using high-resolution and $4d\ensuremath{-}4f$ resonant photoemission spectroscopies. The electronic structure of this material has been studied over a wide temperature range, and hybridization between $f$ and conduction electrons can be clearly observed to form a Kondo resonance near the Fermi level at low temperatures. The characteristic temperature of the localized-to-itinerant transition is around 120 K, which is much higher than its coherence temperature ${T}_{\text{coh}}\ensuremath{\sim}30\phantom{\rule{0.28em}{0ex}}\mathrm{K}$.