Relativistic band-structure calculations for CeTIn5 (T = Ir and Co) and analysis of the energy bands by using tight-binding method

In order to investigate electronic properties of recently discovered heavy fermion superconductors CeTIn5 (T = Ir and Co), we employ the relativistic linear augmented-plane-wave (RLAPW) method to clarify the energy band structures and Fermi surfaces of those materials. The obtained energy bands mainly due to the large hybridization between Cc 4f and In 5p states well reproduce the Fermi surfaces consistent with the de Haas-van Alphen experimental results. However, when we attempt to understand magnetism and superconductivity in CeTIn5 from the microscopic viewpoint, the energy bands obtained in the RLAPW method are too complicated to analyze the system by further including electron correlations. Thus, it is necessary to prepare a more simplified model, keeping correctly the essential characters of the energy bands obtained in the band-structure calculation. For the purpose, we construct a tight-binding model for CeTIn5 by including f-f and p-p hoppings as well as f-p hybridization, which are expressed by the Slater-Koster integrals, determined by the direct comparison with the band-calculation result. Similarity and difference between CeIrIn5 and CeCoIn5 are discussed based on the obtained tight-binding model, suggesting a significant importance of the effect of crystalline electric field to understand the difference in electronic properties among CeTIn5.