An dynamical-mean-field-theory investigation of specific heat and electronic structure of $\alpha$ and $\delta$-plutonium

TL;DR

This study uses dynamical mean field theory to compare the electronic structure and specific heat of $ ext{α}$ and $ ext{δ}$-plutonium, revealing the importance of electronic correlations in explaining experimental observations.

Contribution

It applies DMFT with different physical models to accurately reproduce the specific heat and electronic structure of plutonium phases, highlighting the role of electronic correlations.

Findings

Enhanced specific heat coefficient in δ-Pu due to strong correlations.

Good agreement of density of states with photoemission spectra.

Contradiction with experiment in the $5f^6$ model predictions.

Abstract

We have carried out a comparative study of the electronic specific heat and electronic structure of $\alpha$ and $\delta$-plutonium using dynmical mean field theory (DMFT). We use the perturbative T-matrix and fluctuating exchange (T-matrix FLEX) as a quantum impurity solver. We considered two different physical pictures of plutonoium. In the first, $5{f^5}+$, the perturbative treatment of electronic correlations has been carried out around the non-magnetic (LDA) Hamiltonian, which results in an f occupation around a bit above $n_f = 5 $. In the second, $5{f^6}-$, plutonium is viewed as being close to an $5{f^6}$ configuration, and perturbation theory is carried out around the (LDA+U) starting point bit below $n_f = 6 $. In the latter case the electronic specific heat coefficient $\gamma$ attains a smaller value in $\gamma$-Pu than in $\alpha$-Pu, in contradiction to experiment, while in the former case our calculations reproduce the experimentally observed large increase of $\gamma$ in $\delta$-Pu as compared to the $\alpha$ phase. This enhancement of the electronic specific heat coefficient in $\delta$-Pu is due to strong electronic correlations present in this phase, which cause a substantial increase of the electronic effective mass, and high density of states at $E_F$. The densities of states of $\alpha$ and $\delta$-plutonium obtained starting from the open-shell configuration are also in good agreement with the experimental photoemission spectra.