Nature of Non-magnetic Strongly-Correlated State in Plutonium
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0986-OO01-07
Nature of Non-Magnetic Strongly-Correlated State in Plutonium Leonid Pourovskii1, Alexander Shick2, Ladislav Havela3, Mikhail Katsnelson4, and Alexander Lichtenstein5 1 Ecole Polytechnique, Centre de Physique Theorique, Paris, 91128, France 2 Department of Condensed Matter Theory, Institute of Physics ASCR, Na Slovance 2, Prague, 182 21, Czech Republic 3 Faculty of Mathematics and Physics, Charles University, Ke Karlovu 5, Prague, Czech Republic 4 Institute for Molecules and Materials, Radbound University, Nijmegen, 6525, Netherlands 5 Department of Physics, University of Hamburg, Jungiusstrasse 9, Hamburg, 20355, Germany
ABSTRACT Ab-initio relativistic dynamical mean-field theory is applied to resolve the long-standing controversy between theory and experiment in the "simple" face-centered cubic phase of plutonium called δ-Pu. In agreement with experiment, neither static nor dynamical magnetic moments are predicted. In addition, the quasiparticle density of states reproduces not only the peak close to the Fermi level, which explains the large coefficient of electronic specific heat, but also main f-features observed in photoelectron spectroscopy and is attributed to f5-f6 configuration fluctuations. INTRODUCTION The solid-state properties of most of elements are now well understood on the basis of quantum physics – with few exceptions, notably the element number 94, plutonium. For Pu, difficulties have been known for many years, hence the large number of studies, especially theoretical, of this mysterious element. Plutonium has six crystalline phases at ambient pressure, some of which are separated by unusual phase transitions (with large discontinuities in volume), exhibit negative thermal expansion coefficients, or form exotic low-symmetry structures [1,2]. The main challenge to explain these anomalous properties is that the characteristic ingredient of actinides, the 5f electronic states, are in the cross-over regime between the localized and delocalized (itinerant) behaviour in Pu [3,4]. The early part of the actinide series with the 5f states being itinerant, i.e. part of the metallic bond, culminates with Pu; starting with Am (Z = 95), the 5f states are localized, non-bonding, and resemble the 4f states in lanthanides. Both itinerant and localized regimes are well covered by existing theories, but they cannot be simply interpolated due to the importance of many-body electron correlations [5,6]. The fundamental problem for Pu is that theories of strongly correlated systems exhibit local magnetic moments (ordered or disordered), whereas experimental data in Pu demonstrate unambiguously their absence [7]. Standard band-structure calculations predict strong magnetism for different phases of Pu [4,8]. and local moments appear as a crucial ingredient for an adequate description of equilibrium lattice constants and bulk moduli [9]. Here we demonstrate the solution to this problem by including dynamical correlation effects, the spin-orbital fluctuations involving f 5 and f 6 corresponding to the mix-va
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