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Register a new userEmergence of quasiparticle multiplets in curium
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A combination of the density functional theory and the single-site dynamical mean-field theory is employed to study the electronic structures of various allotropes of elemental curium (Cm-I, Cm-II, and Cm-III). We find that the 5$f$ valence electrons in the high-symmetry Cm-I and Cm-II phases remain localized, while they turn into itinerancy in the low-symmetry monoclinic Cm-III phase. In addition, conspicuous quasiparticle multiplets are identified in the 5$f$ electronic density of states of the Cm-III phase. We believe that it is the many-body transition between $5f^{7}$ and $5f^{8}$ configurations that gives rise to these quasiparticle multiplets. Therefore, the Cm-III phase is probably a new realization of the so-called Racah metal.
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The ground state electronic structure and magnetic behaviors of curium dioxide (CmO$_{2}$) are controversial. In general, the formal valence of Cm ions in CmO$_{2}$ should be tetravalent. It implies a $5f^{6.0}$ electronic configuration and a non-magnetic ground state. However, it is in sharp contrast with the large magnetic moment measured by painstaking experiments. In order to clarify this contradiction, we tried to study the ground state electronic structure of CmO$_{2}$ by means of a combination of density functional theory and dynamical mean-field theory. We find that CmO$_{2}$ is a wide-gap charge transfer insulator with strong 5$f$ valence state fluctuation. It belongs to a mixed-valence compound indeed. The predominant electronic configurations for Cm ions are $5f^{6.0}$ and $5f^{7.0}$. The resulting magnetic moment agrees quite well with the experimental value. Therefore, the magnetic puzzle in CmO$_{2}$ can be appropriately explained by the mixed-valence scenario.
We use Ru $L_3$-edge (2838.5 eV) resonant inelastic x-ray scattering (RIXS) to quantify the electronic structure of Ca$_2$RuO$_4$, a layered $4d$-electron compound that exhibits a correlation-driven metal-insulator transition and unconventional antiferromagnetism. We observe a series of Ru intra-ionic transitions whose energies and intensities are well described by model calculations. In particular, we find a $rm{J}=0rightarrow 2$ spin-orbit excitation at 320 meV, as well as Hunds-rule driven $rm{S}=1rightarrow 0$ spin-state transitions at 750 and 1000 meV. The energy of these three features uniquely determines the spin-orbit coupling, tetragonal crystal-field energy, and Hunds rule interaction. The parameters inferred from the RIXS spectra are in excellent agreement with the picture of excitonic magnetism that has been devised to explain the collective modes of the antiferromagnetic state. $L_3$-edge RIXS of Ru compounds and other $4d$-electron materials thus enables direct measurements of interactions parameters that are essential for realistic model calculations.
We demonstrate that a theoretical framework fully incorporating intra-atomic correlations and multiplet structure of the localized 4f states is required in order to capture the essential physics of rare-earth semiconductors and semimetals. We focus in particular on the rare-earth semimetal erbium arsenide (ErAs), for which effective one-electron approaches fail to provide a consistent picture of both high and low-energy electronic states. We treat the many-body states of the Er 4f shell within an atomic approximation in the framework of dynamical mean-field theory. Our results for the magnetic-field dependence of the 4f local moment, the influence of multiplets on the photoemission spectrum, and the exchange splitting of the Fermi surface pockets as measured from Shubnikov-de Haas oscillations, are found to be in good agreement with experimental results.
An easily accessible method is presented that permits to calculate spectra involving atomic multiplets relevant to X-ray Absorption Spectroscopy (XAS) and Resonant Inelastic X-ray Scattering (RIXS) experiments. We present specific examples and compare the calculated spectra with available experimental data
The physical properties of plutonium and plutonium-based intermetallic compounds are extremely sensitive to temperature, pressure, and chemical alloying. A celebrated example is the high-temperature $delta$ phase plutonium, which can be stabilized at room temperature by doping it with a few percent trivalent metal impurities, such as gallium or aluminum. The cubic phase Pu$_{3}$Ga, one of the plutonium-gallium intermetallic compounds, plays a key role in understanding the phase stability and phase transformation of the plutonium-gallium system. Its electronic structure might be essential to figure out the underlying mechanism that stabilizes the $delta$ phase plutonium-gallium alloy. In the present work, we studied the temperature-dependent correlated electronic states of cubic phase Pu$_{3}$Ga by means of a combination of the density functional theory and the embedded dynamical mean-field theory. We identified orbital selective 5$f$ itinerant-localized (coherent-incoherent) crossovers which could occur upon temperature. Actually, there exist two well-separated electronic coherent temperatures. The higher one is for the $5f_{5/2}$ state [$T_{text{coh}}(5f_{5/2}) approx 700$ K], while the lower one is for the $5f_{7/2}$ state [$T_{text{coh}}(5f_{7/2}) approx 100$ K]. In addition, the quasiparticle multiples which originate from the many-body transitions among the $5f^{4}$, $5f^{5}$, and $5f^{6}$ electronic configurations, decay gradually. The hybridizations between the localized 5$f$ bands and conduction bands are subdued by high temperature. Consequently, the Fermi surface topology is changed, which signals a temperature-driven electronic Lifshitz transition. Finally, the calculated linear specific heat coefficient $gamma$ is approximately 112 mJ / (mol K$^2$) at $T = 80$ K.
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