Sommerfeld coefficient ofδ-Pu determined via a low-temperature specific heat Pu-Ce study

Abstract

Low-temperature specific-heat experiments on ␦-Pu stabilized by Ce give the value of the Sommerfeld coefficient ␥ in the close vicinity of 40 mJ/ mol K 2 . The most precise data set for Pu-6.1 at. % Ce yields ␥ = ͑41.5Ϯ 0.5͒ mJ/ mol K 2 and the Debye temperature D = ͑103.0Ϯ 0.5 K͒. As Ce is in a compressed ␣-Ce state, major contribution to the ␥ value comes from the Pu states. Theoretical calculations suggest that the 5f 6 admixture in the 5f 5 ground state is responsible for the high-␥ value. Although the 5f states are not present at the Fermi level, low-energy excitations due to transitions of the 5f 6 → 5f 5 type contribute to the spectral density around the Fermi level.

Bulk properties and photoelectron spectroscopy of the ζ-U–Pu phase

“…For example, the spectra for 69% Pu are practically identical to pure Pu deposited under the same conditions, and the variation for 47% Pu is only minor. actually data obtained on Pu-6.1 at.% Ce [15], which are in tbe low-T range more reliable than those from Ref. [16], obtained on Al stabilized d-Pu.…”

“…The first inspection of the data (see Fig. 2) in the C p /T vs. T representation reveals that the Debye temperatures H D are somewhat higher than for d-Pu alloys (H D % 100 K) [14] while the Sommerfeld coefficient of electronic specific heat c is somewhat lower than that for d-Pu, being close to 40 mJ/mol K 2 [14,15]. Comparing the two U-Pu alloys, the one with higher Pu concentration has a higher c-value and lower H D .…”

Correlation strength and orbital differentiation across the phase diagram of plutonium metal

“…δ-Pu has the largest coefficient among the highsymmetry phases, with γ of around 297 mJmol −1 K −2 which is overestimated in comparison to the experimental values of 43 -64 mJmol −1 K −2 . 4,6,7 Besides the similar quasiparticles weights, γ-Pu has also a large specific heat coefficient of 273.9 mJmol −1 K −2 . It is important to mention that the other high-symmetry phases have much smaller coefficients, where δ ′ -Pu has the minimum γ of 114 mJmol −1 K −2 .…”

“…Upon heating the β phase undergoes a structural transition to the γ phase, which is a face centered orthorombic structure, followed by δ, δ ′ , and ǫ phases. 3 The δ phase has been the subjected of most theoretical studies, and was regarded as its most exotic properties, such as the "missing magnetism", 4,5 large specific heat, 6,7 and negative thermal expansion which is also observed in δ ′ phase. 3 Density functional theory (DFT), and its extensions to magnetic systems such as spin density functional theory target ground state properties.…”

5f Magnetism—Specific Features And Boundaries

“…Within this concept it is difficult to understand, why even the volume expanded δ-Pu phase has practically the same value of Pauli susceptibility as the low-volume phases, although the Sommerfeld coefficient γ reaching 40 mJ/mol K 2 points to strong e-e correlations [3]. The 5f occupancy exceeding n 5f = 5.0 seems to be clue for the lack of magnetism [4].…”