Studying the local moment and 5$f$-electron occupations sheds insight into the electronic behavior in actinide materials. X-ray absorption spectroscopy (XAS) has been a powerful tool to reveal the valence electronic structure when assisted with theoretical calculations. However, the analysis currently taken in the community on the branching ratio of the XAS spectra generally does not account for the hybridization effects between local $f$-orbitals and conduction states. In this paper, we discuss an approach which employs the DFT+Gutzwiller rotationally-invariant slave boson (DFT+GRISB) method to obtain a local Hamiltonian for the single-impurity Anderson model (SIAM), and calculates the XAS spectra by the exact diagonalization (ED) method. A customized numerical routine was implemented for the ED XAS part of the calculation. By applying this technique to the recently discovered 5$f$-electron topological Kondo insulator PuB$_4$, we determined the signature of 5$f$-electronic correlation effects in the theoretical X-ray spectra. We found that the Pu 5$f$-6$d$ hybridization effect provides an extra channel to mix the $j=5/2$ and $7/2$ orbitals in the 5$f$ valence. As a consequence, the resulting electron occupation number and spin-orbit coupling strength deviate from the intermediate coupling regime.
In order to promote our understanding on electronic structure of actinide dioxides, we construct a tight-binding model composed of actinide $5f$ and oxygen $2p$ electrons, which is called $f$-$p$ model. After the diagonalization of the $f$-$p$ model, we compare the eigenenergies in the first Brillouin zone with the results of relativistic band-structure calculations. Here we emphasize a key role of $f$-$p$ hybridization in order to understand the electronic structure of actinide dioxides. In particular, it is found that the position of energy levels of $Γ_7$ and $Γ_8$ states determined from cr…
The local-density approximation combined with the dynamical mean-field theory (LDA+DMFT) is applied to the paramagnetic phase of light actinide dioxides: UO2, NpO2, and PuO2. The calculated band gaps and the valence-band electronic structure are in a very good agreement with the optical absorption experiments as well as with the photoemission spectra. The hybridization of the actinide 5f shell with the 2p states of oxygen is found to be relatively large, it increases the filling of the 5f orbitals from the nominal ionic configurations with two, three, and four electrons to nearly half-integer …
We present a detailed analysis of the one-electron physics of the actinides. Various LMTO basis sets are analyzed in order to determine a robust bare Hamiltonian for the actinides. The hybridization between f- an spd- states is compared with the f-f hopping in order to understand the Anderson-like and Hubbard-like contributions to itineracy in the actinides. We show that both contributions decrease strongly as one move from the light actinides to the heavy actinides, while the Anderson-like contribution dominates in all cases. A real-space analysis of the band structure shows that nearest-neig…
The hybridization between the localized 4$f$ level ($f$) with conduction ($c$) states in $γ$-Ce upon cooling has been previously revealed in single crystalline thin films experimentally and theoretically, whereas its influence on the $γ\rightarrowα$ phase transition was not explicitly verified, due to the fact that the phase transition happened in the bulk-layer, leaving the surface in the $γ$ phase. Here in our work, we circumvent this issue by investigating the effect of alloying addition of La on Ce, by means of crystal structure, electronic transport and ARPES measurements, together with a…
Actinide elements produce a plethora of interesting physical behaviors due to the 5f states. This review compiles and analyzes progress in understanding of the electronic and magnetic structure of the 5f states in actinide metals. Particular interest is given to electron energy-loss spectroscopy and many-electron atomic spectral calculations, since there is now an appreciable library of core d -> valence f transitions for Th, U, Np, Pu, Am, and Cm. These results are interwoven and discussed against published experimental data, such as x-ray photoemission and absorption spectroscopy, transport …
The heavy fermion state with Kondo-hybridization (KH), usually manifested in f-electron systems with lanthanide or actinide elements, was recently discovered in several 3d transition metal compounds without f-electrons. However, KH has not yet been observed in 4d/5d transition metal compounds, since more extended 4d/5d orbitals do not usually form flat bands that supply localized electrons appropriate for Kondo pairing. Here, we report a doping- and temperature-dependent angle-resolved photoemission study on 4d Ca2-xSrxRuO4, which shows the signature of KH. We observed a spectral weight transf…
We study the spin-dependent electronic structure of UTe and UT_{2}Si_{2} (T=Cu and Mn) compounds with a combination of x-ray magnetic circular dichroism measurements and first principle calculations. By exploiting the presence of sizable quadrupolar and dipolar contributions to the U L_{2,3}-edge x-ray absorption cross section we are able to provide unique information on the extent of hybridization between 5f and 6d/3d electronic states, a key parameter regulating the physical properties of all actinide materials. Since this information is hardly accessible to other probes, the new methodology…
Although strong electronic correlations are known to be responsible for some highly unusual behaviors of solids such as, metal--insulator transitions, magnetism and even high--temperature superconductivity, their interplay with recently discovered topological states of matter awaits full exploration. Here we use a modern electronic structure method combining density functional theory of band electrons with dynamical self-energies of strongly correlated states to predict that two well-known phases of actinide compound UNiSn, a paramagnetic semiconducting and antiferromagnetic metallic, correspo…
In heavy-fermion compounds, f electrons show both itinerant and localized behaviour depending on the external conditions, and the hybridization between localized f electrons and itinerant conduction bands gives rise to their exotic properties like heavy-fermions, magnetic orders and unconventional superconductivity. Duo to the risk of handling radioactive actinide materials, the direct experimental evidence of the band structure evolution across the localized-itinerant and magnetic transitions for 5f electrons is lacking. Here, by using angle-resolved photoelectron spectroscopy, we revealed th…
Heavy-fermion materials are mostly rare-earth or actinide intermetallics with very few exceptions in d-electron systems. The physical mechanism for these d-electron heavy fermion systems remains unclear. Here by studying the quadruple-perovskite CaCu3Ir4O12, we propose a symmetry-based mechanism that may enforce heavy-fermion physics in d-electron systems. We show that electron hoppings between neighboring Cu 3d-orbitals are strictly prohibited by the crystal symmetry, so that Cu 3d-electrons can only become delocalized through hybridization with other more itinerant bands, resembling that in …
Based on its condensed-matter properties, crystal structure, and metallurgy, which includes a phase diagram with six allotropic phases, plutonium is one of the most complicated pure elements in its solid state. Its anomalous properties, which are indicative of a very strongly correlated state, are related to its special position in the periodic table, which is at the boundary between the light actinides that have itinerant 5$f$ electrons and the heavy actinides that have localized 5$f$ electrons. As a foundational study to probe the role of local electronic correlations in Pu, we use the local…
In a large number of rare-earth and actinide systems, Kondo effect tends to suppress magnetic order by making the spin singlet between localized and conduction electron spins. In the presence of orbital degrees of freedom, however, there emerge exotic electronic orders induced by Kondo effect. The orbital Kondo effect can collectively make diagonal and off-diagonal (superconducting) orders. With the particle-hole symmetry in conduction bands, these orders are all degenerate, forming a macroscopic SO(5) multiplet. This paper discusses recent theoretical development on these electronic orders wh…
