From antiferromagnetic and hidden order to Pauli paramagnetism in UM2Si2 compounds with 5f electron duality

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Using inelastic X-ray scattering beyond the dipole limit and hard X-ray photoelectron spectroscopy we establish the dual nature of the U 5f electrons in UM2Si2 (M = Pd, Ni, Ru, Fe), regardless of their degree of delocalization. We have observed that the compounds have in common a local atomic-like state that is well described by the U 5f2 configuration with the Γ(1)1and Γ2 quasi-doublet symmetry. The amount of the U 5f3 configuration, however, varies considerably across the UM2Si2 series, indicating an increase of U 5f itineracy in going from M = Pd to Ni to Ru and to the Fe compound. The identified electronic states explain the formation of the very large ordered magnetic moments in UPd2Si2 and UNi2Si2, the availability of orbital degrees of freedom needed for the hidden order in URu2Si2 to occur, as well as the appearance of Pauli paramagnetism in UFe2Si2. A unified and systematic picture of the UM2Si2 compounds may now be drawn, thereby providing suggestions for additional experiments to induce hidden order and/or superconductivity in U compounds with the tetragonal body-centered ThCr2Si2 structure.

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