Collapse of quasiparticle multiplets and $5f$ itinerant-localized crossovers in cubic phase Pu$_{3}$Ga

Abstract

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.