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Register a new userElectronic Correlation Induced Expansion of Compensated Electron and Hole Fermi Pockets in delta-Plutonium
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Plutonium is a critically important material as the behavior of its 5f-electrons stands midway between the metallic-like itinerant character of the light actinides and localized atomic-core-like character of the heavy actinides. The delta-phase of plutonium (delta-Pu), while still itinerant, has a large coherent Kondo peak and strong electronic correlations coming from its near-localized character. Using sophisticated Gutwiller wavefunction and dynamical mean-field theory correlated theories, we study for the first time the Fermi surface and associated mass renormalizations of delta-Pu together with calculations of the de Haas-van Alphen (dHvA) frequencies. We find a large (200%) correlation-induced volume expansion in both the hole and electron pockets of the Fermi surface in addition to an intermediate mass enhancement. All of the correlated electron theories predict, approximately, the same hole pocket placement in the Brillouin zone, which is different from that obtained in conventional density-functional band-structure theory, whereas the electron pockets from all theories are in, roughly, the same place.
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An understanding of the phase diagram of elemental plutonium (Pu) must include both the effects of the strong directional bonding and the high density of states of the Pu 5f electrons, as well as how that bonding weakens under the influence of strong electronic correlations. We present for the first time electronic-structure calculations of the full 16-atom per unit cell alpha-phase structure within the framework of density functional theory (DFT) together with dynamical mean-field theory (DMFT). Our calculations demonstrate that Pu atoms sitting on different sites within the alpha-Pu crystal structure have a strongly varying site dependence of the localization-delocalization correlation effects of their 5f electrons and a corresponding effect on the bonding and electronic properties of this complicated metal. In short, alpha-Pu has the capacity to simultaneously have multiple degrees of electron localization/delocalization of Pu 5f electrons within a pure single-element material.
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We investigate the electronic states of a one-dimensional two-orbital Hubbard model with band splitting by the exact diagonalization method. The Luttinger liquid parameter $K_{rho}$ is calculated to obtain superconducting (SC) phase diagram as a function of on-site interactions: the intra- and inter-orbital Coulomb $U$ and $U$, the Hund coupling $J$, and the pair transfer $J$. In this model, electron and hole Fermi pockets are produced when the Fermi level crosses both the upper and lower orbital bands. We find that the system shows two types of SC phases, the SC Roman{u-large} for $U>U$ and the SC Roman{u-large} for $U<U$, in the wide parameter region including both weak and strong correlation regimes. Pairing correlation functions indicate that the most dominant pairing for the SC Roman{u-large} (SC Roman{u-large}) is the intersite (on-site) intraorbital spin-singlet with (without) sign reversal of the order parameters between two Fermi pockets. The result of the SC Roman{u-large} is consistent with the sign-reversing s-wave pairing that has recently been proposed for iron oxypnictide superconductors.
We have measured the heat capacities of $delta-$Pu$_{0.95}$Al$_{0.05}$ and $alpha-$Pu over the temperature range 2-303 K. The availability of data below 10 K plus an estimate of the phonon contribution to the heat capacity based on recent neutron-scattering experiments on the same sample enable us to make a reliable deduction of the electronic contribution to the heat capacity of $delta-$Pu$_{0.95}$Al$_{0.05}$; we find $gamma = 64 pm 3$ mJK$^{-2}$mol$^{-1}$ as $T to 0$. This is a factor $sim 4$ larger than that of any element, and large enough for $delta-$Pu$_{0.95}$Al$_{0.05}$ to be classed as a heavy-fermion system. By contrast, $gamma = 17 pm 1$ mJK$^{-2}$mol$^{-1}$ in $alpha-$Pu. Two distinct anomalies are seen in the electronic contribution to the heat capacity of $delta-$Pu$_{0.95}$Al$_{0.05}$, one or both of which may be associated with the formation of the $alpha-$ martensitic phase. We suggest that the large $gamma$-value of $delta-$Pu$_{0.95}$Al$_{0.05}$ may be caused by proximity to a quantum-critical point.
We report the three-dimensional (3-D) momentum-resolved soft x-ray photoemission spectroscopy of the Fermi liquid LaNiO$_3$. The out-of-plane and in-plane cuts of the 3-D electron- and hole-Fermi surfaces (FSs) are observed by energy- and angle- dependent photoemission measurements. The energy bands forming the electron FS suggest an $omega^2$ dependence of the imaginary part of the self-energy and a `correlation kink at an energy scale of 0.25 eV. In contrast, the bands which form nesting character hole FSs do not show kinks and match local density approximation calculations. The results indicate a momentum-dependent mass renormalization, leading to electron-hole asymmetry in strongly correlated LaNiO$_3$.
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