Electronic structure of the Pu-based superconductor PuCoGa5 and of related actinide-115 compounds

Abstract

We report a theoretical investigation of the electronic structure of the plutonium-based medium-high-Tc superconductor PuCoGa5, on the basis of ab initio local spin-density functional calculations. We furthermore report electronic structure calculations of the related actinide compounds PuRhGa5, PuIrGa5, UCoGa5, NpCoGa5, and AmCoGa5. PuRhGa5 is a superconductor as well, whereas the other materials do not become superconducting. The equilibrium lattice parameters within the tetragonal HoCoGa5 crystal structure are well reproduced for UCoGa5, NpCoGa5, as well as for the three isoelectronic Pu−115 compounds when we assume delocalized 5f states. The possibility of a partial 5f localization occurring for the Pu−115 compounds is discussed. The electronic structures of the three Pu−115 compounds are computed to be rather similar: in each of the Pu−115 materials the density of states at the Fermi energy is dominated by the Pu 5f contribution. Our total-energy calculations predict antiferromagnetic order to be favorable for all three Pu−115 materials, which is, however, observed experimentally for PuIrGa5 only. Within the Pu−115 series some small changes of the bands near the Fermi energy occur, which could be relevant for the superconductivity. A comparison of the ab initio calculated and the experimental properties clearly supports the picture of delocalized 5f electrons for UCoGa5. The neptunium-based 115 compound is predicted to order antiferromagnetically, which is supported by experiment. Also, the calculated magnetic moment (0.85μB) compares well with the measured moment (0.84μB). These findings advocate that the Np 5f’s are still to some extent delocalized in NpCoGa5. In contrast, for the Am−115 analog the Am 5f electrons can be expected to be localized. We furthermore discuss the theoretical Fermi surfaces and present calculated de Haas-van Alphen quantities for a comparison with future experiments. For UCoGa5 we obtain a semi-quantitative agreement with recently reported de Haas-van Alphen experiments. The possible origins of the superconductivity are discussed. Our investigation particularly reinforces the analogy to the heavy-fermion superconductors CeCoIn5 and CeIrIn5, however, with a stronger coupling strength due to a much stronger 5f hybridization.

Source-reported materials — not catalogue approval

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