Signatures of Non-integer 5f Occupancy in Pu Systems: Magnetic Properties and Photoelectron Spectroscopy Studies
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1104-NN08-05
Signatures of Non-integer 5f Occupancy in Pu Systems: Magnetic Properties and Photoelectron Spectroscopy Studies Ladislav Havela1, Alexander Shick2, Thomas Gouder3, Franck Wastin3, and Jean Rebizant3 1 Department of Electronic Structures, Charles University, Ke Karlovu 5, Prague 2, CZ-12116, Czech Republic 2 Institute of Physics, Academy of Sciences of the Czech Republic, Prague 8, CZ-18221, Czech Republic 3 European Commission, Joint Research Centre, Institute for Transuranium Elements, Postfach 2340, Karlsruhe 1, D-76125, Germany ABSTRACT Very diverse Pu compounds exhibit strikingly universal features in their valence-band photoemission (PES) spectra. The conjecture that such features represent the 5f 5 final state multiplet has been corroborated by LDA+Hubbard I calculations, meaning that the ground state has a mixed 5f 5-5f 6 character. Later on, more elaborated DMFT techniques (one crossing approximation, QMC) led to similar conclusions, providing quantitative explanation of such intermeate-valent situation in more details. Analogies in PES spectra of δ-Pu and other Pu systems suggest that the situation envisaged for δ-Pu is relevant for a large group of Pu compounds. Here we show that the around mean field LDA+U in conjunction with the Hubbard I approximation, which describes well the non-magnetic ground state for δ-Pu, captures in reality properties of a large group of Pu (as well as e.g. Am) compounds, reproducing correctly the onset of magnetism and size of magnetic moments.
INTRODUCTION Description of the character of 5f electrons in δ-Pu has a pivotal role in the understanding of light actinides at the verge of localization. There have recently appeared several ambitious concepts aiming at many-body affects beyond conventional band structure calculations [1,2]. In addition, more conventional GGA+orbital polarization is still being applied [3], with the belief that error manifest in the magnetic ground state obtained does not affect much density of states. The focus on δ-Pu leads to a neglecting, to some degree, of other Pu-based systems. Here we want to show that extending the scope, which will now include intermetallic compounds and also other compounds as pnictides and chalcogenides, a new landscape will emerge, on which some characteristics as onset of magnetic ordering and variations in valence-band PES spectra can be understood assuming a variable 5f occupancy, n5f, which adopts values exceeding 5.0, determined essentially by bonding conditions. The loss of magnetism appears then not as an individual trait of δ-Pu or other Pu phases, but as a systemic and robust behavior belonging to a broad regime. The picture, which differs somewhat from a traditional view of Pu as the element with 5 5f electrons, gets a sound support from realistic LDA+U calculations [4,5]. On the other hand, recent spectroscopic data (XAS, EELS) show that n5f should not be much higher than 5.0 [6]. Therefore the issue of the 5f occupancy seems to be the manifestation of the lack of consensus about the correct descr
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