Hybridization Effects Revealed by Angle-Resolved Photoemission Spectroscopy in Heavy-Fermion Ce_2IrIn_8

We utilize high-resolution resonant angle-resolved photoemission spectroscopy (ARPES) to study the band structure and hybridization effect of the heavy-fermion compound Ce_2IrIn_8. We observe a nearly flat band at the binding energy of 7 meV below the coherent temperature T_\rm coh\sim 40 K, which characterizes the electrical resistance maximum and indicates the onset temperature of hybridization. However, the Fermi vector and the Fermi surface volume have little change around T_\rm coh, which challenges the widely believed evolution from a high-temperature small Fermi surface to a low-temperature large Fermi surface. Our experimental results of the band structure fit well with the density functional theory plus dynamic mean-field theory calculations.