Relocalization of uranium 5f electrons in the antiferromagnetic heavy-fermion superconductor UPd2Al3 : Insights from angle-resolved photoemission spectroscopy

We investigate the antiferromagnetic heavy fermion superconductor UPd₂Al₃, employing angle-resolved photoemission spectroscopy to unravel the complex electronic structure of its U $5f$ electrons. We observe unexpected characteristics that challenge the conventional temperature-dependent behavior of heavy fermion systems, revealing unexpected characteristics. At temperatures above the anticipated coherence temperature (T*), we observe itinerant U $5f$ electrons at temperatures higher than previously postulated. Additionally, a previously unidentified dispersionless band emerges around 600 meV below the Fermi energy, potentially linked to spin-orbit splitting within the U $5f$ states. Hybridization between the $5f$ electrons and conduction band was observed with an energy dispersion of 10 meV at low temperatures, suggesting that U $5f$ electrons near and at the Fermi surface have an itinerant nature. Temperature-dependent 5d-5f resonance spectra reveal that the $5f$ electron spectrum weight increases with lowering temperature and begins to decrease at temperatures significantly higher than the N\'eel temperature (TN). We further show that the competition between the Kondo effect and Ruderman-Kittel-Kasuya-Yosida (RKKY) interactions may be responsible for the relocalization of $5f$ electrons, making relocalization a precursor to the establishment of magnetic order at lower temperatures. Our experiments also provide evidence that $5f$ electrons with the same orbital are involved in both the Kondo effect and RKKY interactions, suggesting that the two coexist at lower temperatures.