We utilized high-resolution resonant angle-resolved photoemission spectroscopy (ARPES) to study the band structure and hybridization effect of the heavy-fermion compound Ce2IrIn8. We observe a nearly flat band at the binding energy of 7 meV below the coherent temperature Tcoh~40 K, which characterizes the electrical resistance maximum indicating the onset temperature of hybridization. However, the Fermi vector kF and the Fermi surface (FS) volume have little change around Tcoh, challenging the widely believed evolution from a high-temperature small FS to a low-temperature large FS. Our experimental results of the band structure fit well with the density functional theory plus dynamic mean-field theory (DFT+DMFT) calculations.
INTRODUCTION:Heavy-fermion compounds, first discovered in CeAl3 in 1975 [1], are some of the most exotic materials in condensed matter physics. The name originates from the largely enhanced effective mass of the heavy quasi-particles, which can be 2 or 3 orders of magnitude higher than that in a normal metal [2]. These compounds usually contain some of Ce, Sm, Yb, U, Pr, Pu, Np elements, which possess an unfilled 4f or 5f shell. It is widely believed that 4f/5f electrons are local moments at high temperatures and become itinerant after hybridized with the conduction electrons at low temperatures. Varieties of phenomena, e.g., antiferromagnetism [3], ferromagnetism [4], superconductivity [5], quantum critical point [6], quadrupole order [7], hidden order [8-9], topological property [10], have been discovered in heavy-fermion compounds. Central to understanding these exotic phenomena is the interplay of itinerancy and localization. However, the low energy scales (critical temperature, hybridization gap, superconducting gap) in heavy-fermion systems have brought major challenges to many experimental techniques.CemTnIn3m+2n (m = 1, 2; n = 1, 2 and T: Co, Rh, Ir, Pd, Pt) family is a good platform of heavy-fermion materials for studying the interplay between c-f hybridization, magnetism, superconductivity, quantum criticality, and etc. CemTnIn3m+2n crystallizes with a tetragonal unit cell that can be viewed as m-layers of CeIn3 unit stacked sequentially with intervening n-layers of TIn2 along the c-axis. Among them, the spin-glass state observed in Ce2IrIn8 indicates partially delocalized Ce 4f electron [11]. The magnetism in Ce2IrIn8 depends on Ce-Ir hybridization and local Ce environment. The small but finite onset temperature for spin freezing rules out the quantum critical point (QCP) scenario in Ce2IrIn8 [11]. High Sommerfeld coefficient (γ~700 mJ/mol‧K 2 ) [12] and the absence of long-range magnetic order indicate an itinerant behavior of Ce 4f electron. μSR observed a 'Knight-shift anomaly' in which the Knight shift constant K no longer scales linearly with the susceptibility below a characteristic temperature Tcoh, in agreement with the "two-fluid" model of heavy-fermion formation [15]. Resistivity measurements showed a broad maximum near 40 -50 K [13,16], manifesting the development of a...
