Electronic structure evolution accompanying heavy fermion formation in Ce[Cu.sub.2][Si.sub.2]

The cooper pairs in the heavy-fermion superconductor Ce[Cu.sub.2][Si.sub.2] are formed of heavy fermions. Therefore, the heavy fermions are fundamental to the emergence of unconventional superconductivity and associated non-Fermi-liquid behavior in the normal state. The interplay between localization and itinerancy manifested on the electronic structure is key for understanding the heavy-fermion behavior. Here, via the first-principle density functional theory (DFT) combined with single-site dynamical mean-field theory (DMFT), we investigate the temperature (T) evolution of the electronic structure of Ce[Cu.sub.2][Si.sub.2] in the normal state, focusing on the role of the 4f states in the low energy regime. Two characteristic temperature scales of this evolution, which accompanied the heavy-fermion formation, are established. The coherence onset temperature is around 130 K, whereas the heavy- fermion band formation temperature is between 40 and 80 K; both characteristic temperature scales are higher than the transport coherence temperature. Furthermore, the heavy-fermion formation is confirmed by calculating its effective mass variation with the temperature. Based on the calculated T-dependent evolution of the 4f orbital occupancy and electronic structure, an explanation on the behavior of the temperature evolution of the correlation strength of Ce[Cu.sub.2][Si.sub.2] is provided. Our results offer a comprehensive microscopic picture of the heavy-fermion formation in Ce[Cu.sub.2][Si.sub.2], which is essential for further understanding the emergent superconducting pairing mechanism. Ce[Cu.sub.2][Si.sub.2], heavy-fermion formation, temperature, electronic structure, DFT+DMFT PACS number(s): 71.20.Eh, 71.27.+a, 74.70.-b