NSLS-II Friday Lunchtime Seminar

Here we performed a combined bulk-sensitive soft x-ray angle-resolved photoemission spectroscopy (ARPES) and Ce 4d-4f resonant ARPES studies of the three parent compounds of the Ce-115 system: CeCoIn5, CeRhIn5, and CeIrIn5. In CeCoIn5, we spectroscopically resolved the development of band hybridization and the Fermi surface expansion over a wide temperature region. Unexpectedly, the localized-to-itinerant transition occurs at surprisingly high temperatures, yet f electrons are still largely localized even at the lowest temperature. These findings point to an unanticipated role played by crystal field excitations in the strange metal behavior of CeCoIn5. In CeRhIn5, we have directly observed a weakly dispersive heavy quasiparticle band in this heavy fermion compound, whose f-electrons are considered most fully localized. Two of the three crystal-electric-field (CEF) split levels of the Ce 4f5/21 states have been observed at 2.5 and 10 meV above the Fermi energy, with distinctive symmetries. The hybridization mainly happens between these states and Rh 4d band near the Brillouin zone center, on the most three-dimensional Fermi pocket. Remarkably, the f electrons start to turn itinerant at the highest sampling temperature, 180 K, a high temperature scale that is known to be consistent with the CEF splitting. In this important heavy fermion compound with antiferromagnetic state, we paint a comprehensive picture of the dual nature of the f electrons. In CeIrIn5, we find similar behaviors of the f electrons with that of CeCoIn5, and the hybridization also starts at much higher temperature than Tk. We also provide the first experimental evidence for 4f7/21 splittings which, in CeIrIn5, split the octet into four doublets. Our results offer a comprehensive and in part, unanticipated experimental picture of the heavy fermion formation, setting the stage for understanding the emergent properties, including unconventional superconductivity, in this and related material