Screening of4fmoments and delocalization in the compressed light rare earths

Abstract

Spin and charge susceptibilities and the 4f n , 4f n−1 , and 4f n+1 configuration weights are calculated for compressed Ce (n = 1), Pr (n = 2), and Nd (n = 3) metals using dynamical mean field theory combined with the local-density approximation. At ambient and larger volumes these trivalent rare earths are pinned at sharp 4f n configurations, their 4f moments assume atomic-limiting values, are unscreened, and the 4f charge fluctuations are small indicating little f state density near the Fermi level. Under compresssion there is dramatic screening of the moments and an associated increase in both the 4f charge fluctuations and static charge susceptibility. These changes are coincident with growing weights of the 4f n−1 configurations, which it is argued are better measures of delocalization than the 4f n+1 weights which are compromised by an increase in the number of 4f electrons caused by rising 6s, 6p bands. This process is continuous and prolonged as a function of volume, with strikingly similarity among the three rare earths, aside from the effects moderating and shifting to smaller volumes for the heavier members. The observed α-γ collapse in Ce occurs over the large-volume half of this evolution, the Pr analog at smaller volumes, and Nd has no collapse.

Phase Diagram and Electronic Structure of Praseodymium and Plutonium

“…For the fcc phase, the LDA þ DMFT results of Ref. [73] are also reported (dots). effect, which occurs also in Ce [35,36].…”

High-pressure studies with x-rays using diamond anvil cells

“…Light rare-earth metals exhibit pressure-driven volume collapses attributable to 4f electron delocalization (e.g., Ce, Pr, and Gd). Their behavior has been approached by various models [512][513][514], and recently by a fully dynamical treatment of correlations in the lattice using dynamical mean-field theory (DMFT) [515]. HP RXES provides detailed information on the 4f electron occupancy as a function of pressure.…”

Theory of resonant x-ray emission spectra in compounds with localized f electrons

“…The pressure evolution of the valence histogram in elemental lanthanides was theoretically investigated with the aid of material-specific dynamical-mean-field theory (DMFT) [2]. Subsequently, RXES measurements at the L edge of praseodymium were performed [5], yielding a very good agreement with the theory.…”

“…A related mechanism that induces an admixture of several configurations in a single 4f shell is hybridization with the other electronic states. Although this hybridization is often essentially negligible at ambient conditions, it can be enhanced by lattice compression that eventually leads to delocalization of the 4f states [2]. In general, the hybridization mixes more than two 4f m configurations, each contributing with some weight w m .…”

“…Subsequently, RXES measurements at the L edge of praseodymium were performed [5], yielding a very good agreement with the theory. Using a theoretical method very similar to [2] it was argued that elemental americium approaches intermediate-valence regime when compressed [6] but L-edge RXES experiments did not detect any sign of this effect [7], possibly due to a limited resolution. Since then, more L-edge RXES measurements of actinide compounds were made [8,9] where extraction of the valence histogram was possible.…”