Microscopic theory of the insulating electronic ground states of the actinide dioxides AnO2(An = U, Np, Pu, Am, and Cm)

Abstract

The electronic states of the actinide dioxides AnO 2 (with An = U, Np, Pu, Am, and Cm) are investigated employing first-principles calculations within the framework of the local density approximation +U (LDA + U ) approach, implemented in a full-potential linearized augmented plane-wave scheme. A systematic analysis of the An-5f states is performed which provides intuitive connections between the electronic structures and the local crystalline fields of the f states in the AnO 2 series. Particularly the mechanisms leading to the experimentally observed insulating ground states are investigated. These are found to be caused by the strong spin-orbit and Coulomb interactions of the 5f orbitals; however, as a result of the different configurations, this mechanism works in distinctly different ways for each of the AnO 2 compounds. In agreement with experimental observations, the nonmagnetic states of plutonium and curium dioxide are computed to be insulating, whereas those of uranium, neptunium, and americium dioxides require additional symmetry breaking to reproduce the insulator ground states, a condition which is met with magnetic phase transitions. We show that the occupancy of the An-f orbitals is closely connected to each of the appearing insulating mechanisms. We furthermore investigate the detailed constitution of the noncollinear multipolar moments for transverse 3q magnetic ordered states in UO 2 and longitudinal 3q high-rank multipolar ordered states in NpO 2 and AmO 2 .

Cluster multipole theory for anomalous Hall effect in antiferromagnets

“…III, we introduce CMP moments as order parameters defined for a cluster of atoms, which is a natural generalization of the local magnetic moments for atoms. The CMP characterizes the non-collinear AFM structure as analogous to the atomic magnetic multipole moments characterizing the local magnetic distribution [24][25][26][27][28][29] . We show that the AHE of Mn 3 Ir and Mn 3 Z is associated with the cluster octupole moments which belong to the same symmetry with the magnetic dipole moments.…”

Magnetic Structure of UO2 and NpO2 by First-Principle Methods

“…considerably higher than in the literature. 47,81,88,121,122 In the density of states (DoS), the valence band maximum (VBM) and conduction band minimum (CBM) are mainly comprised of uranium f-states. The U d-states are significantly higher in energy and should therefore have very little influence on bonding interactions.…”

“…In terms of the electronic structure, the f-f Mott-Hubbard insulating character of UO2 with a band-gap of 2.00-2.50 eV 2, 76, 77 has been established by optical adsorption, 2, 77 X-ray adsorption (XAS), 3,76,78 X-ray photoemission (XPS), [79][80][81][82] bremsstrahlung isochromatic spectroscopy (BIS), 81,82 resonant photoemission spectroscopy (RPES), 83 inverse photoemission spectroscopy (IPES) 84 and theoretical methods. 47,85,86 In the past, multiple investigations of UO2 have focused on the Fm3 ̅ m (No. 225) crystal structure.…”

“…9,33,41,[48][49][50][51][52][53][54][55][56][57][58][59][60] In addition, although the importance of spin-orbit interactions (SOI) 13 for the treatment of the actinide elements has been highlighted in numerous investigations, 32,47 few consider SOI effects in their fully relativistic studies. 33,45,47,[58][59][60][61] The magnetic structure of UO2 displays interesting characteristics. In the Russel-Saunders (low-spin) coupling scheme, the ground-state of the U 4+ ion is a 3 H4 (Γ5 triplet) multiplet.…”

Slave Boson Theory of Orbital Differentiation with Crystal Field Effects: Application toUO2

“…(5)), but in the entire RISB Fock space H SB [17]. [18][19][20][21][22][23] Operatorial formulation of RISB theory:-The operatorsR Riaα defined above are constructed in such a way that c † Riα are a representation in the physical RISB subspace of the corresponding original fermionic operators c † Riα . However, this construction is not unique.…”