Superconductor PuCoGa5 Research Articles

Self-consistent modeling of thermal and elastic properties of unconventional superconductor PuCoGa5

A self-consistent thermodynamic model of PuCoGa5 is developed, which for the first time takes into account the anharmonicity of both acoustic phonons, described within a Debye model, and optical phonons, considered in an Einstein approximation. Within the framework of this model, we have calculated the temperature dependencies of lattice contributions to heat capacity, bulk modulus, volumetric coefficient of thermal expansion, Debye and Einstein temperatures and their Grüneisen parameters. The electronic heat capacity of PuCoGa5 is obtained, which demonstrates an unusual temperature dependence with two maxima. In addition, it is shown that an abnormal low temperature behavior of the bulk modulus of PuCoGa5 is not caused by the effects of lattice anharmonicity and is most likely due to the valence fluctuations, which is in agreement with previous studies.

Endohedral gallide cluster superconductors and superconductivity in ReGa5

We present transition metal-embedded (T@Gan) endohedral Ga-clusters as a favorable structural motif for superconductivity and develop empirical, molecule-based, electron counting rules that govern the hierarchical architectures that the clusters assume in binary phases. Among the binary T@Gan endohedral cluster systems, Mo8Ga41, Mo6Ga31, Rh2Ga9, and Ir2Ga9 are all previously known superconductors. The well-known exotic superconductor PuCoGa5 and related phases are also members of this endohedral gallide cluster family. We show that electron-deficient compounds like Mo8Ga41 prefer architectures with vertex-sharing gallium clusters, whereas electron-rich compounds, like PdGa5, prefer edge-sharing cluster architectures. The superconducting transition temperatures are highest for the electron-poor, corner-sharing architectures. Based on this analysis, the previously unknown endohedral cluster compound ReGa5 is postulated to exist at an intermediate electron count and a mix of corner sharing and edge sharing cluster architectures. The empirical prediction is shown to be correct and leads to the discovery of superconductivity in ReGa5. The Fermi levels for endohedral gallide cluster compounds are located in deep pseudogaps in the electronic densities of states, an important factor in determining their chemical stability, while at the same time limiting their superconducting transition temperatures.

Electronic structure of the PuCoIn5 compound

The electronic structure of the new superconductor PuCoIn5 has been examined within the LDA+U+SO method taking into account both strong electron correlations and spin-orbit coupling between 5f electrons of an actinide metal. As compared to the characteristics of the known superconductor PuCoGa5, Pu 5f states in PuCoIn5 are more localized but with an intermediate type of coupling between 5f electrons with a strong prevalence of the LS type. However, at a small volume corresponding to the volume of the unit cell of the PuCoGa5 superconductor, the electronic and spectral characteristics of PuCoIn5 are close to the corresponding parameters of PuCoGa5. It has been shown that the occupancy of Co 3d states in PuCoIn5 is close to the previously estimated limiting values providing the optimal doping regime in the electron subsystem of super-conductors of the Pu-115 series.

Single crystal growth, transport, and electronic band structure of YCoGa5

Single crystal of YCoGa5 has been grown via Ga self-flux. In this paper, we report the single crystal growth, crystallographic parameters, resistivity, heat capacity, and band structure results of YCoGa5. YCoGa5 accommodates the HoCoGa5 type structure (space group P4/mmm (No. 123), Z = 1, a = 4.2131(6) Å, c = 6.7929(13) Å, which is isostructural to the extensively studied heavy fermion superconductor system CeMIn5 (M = Co, Rh, Ir) and the unconventional superconductor PuCoGa5 with Tc = 18.5 K. No superconductivity is observed down to 1.75 K. Band structure calculation results show that its band at the Fermi level is mainly composed of Co-3d and Ga-4p electrons states, which explains its similarity of physical properties to YbCoGa5 and LuCoGa5.

Relaxation of Photoinduced Quasi-Particles in Correlated Electron Metals

We present our studies of photoinduced quasi-particle dynamics in correlated electron metals. At room temperature, these materials exhibit metallic behavior characterized by the presence of a Fermi surface. Electronic correlations lead to a modification of the low-energy electronic structure near the Fermi level resulting in the opening of gaps or partial gaps due to such phenomena as density waves or superconductivity. We describe the results of optical pump-probe studies of quasi-particle dynamics in the spin density wave metal UNiGa5, the heavy-fermion superconductor PuCoGa5, and the pnictide high-temperature superconductor (Ba,K)Fe2As2.

Effect of Coulomb Correlations on the Electronic Structure ofPuCoGa5

We investigate the effect of strong Coulomb correlations on the electronic structure of the Pu-based superconductor PuCoGa5 by employing the relativistic local spin density approximation+ Hubbard U (LSDA+U) method. The inclusion of intra-atomic Coulomb U and exchange J parameters leads to a significant reconstruction of the f states electronic structure over that given by the LSDA approach. At variance with the LSDA, the LSDA+U suggests "jj"-like coupling for the Pu 5f manifold.

Electronic Structure of PuCoGa5 and UCoGa5

AbstractThe electronic structure of the Pu-based superconductor PuCoGa5 and the Pauli paramagnet UCoGa5 is investigated using photoemission spectroscopy. The photoemission data of PuCoGa5 reveal features at the Fermi energy EF and about 1-1.5 eV below EF indicative of itinerant and localized f-electrons, respectively. Angle-resolved spectra of UCoGa5 show two peaks at similar energies that are highly dispersive, providing evidence for itinerant character of the f-electrons in this material. A comparison of the PuCoGa5 and UCoGa5 data to the spectra of α-Pu and δ-Pu serves to place PuCoGa5 within the context of the more general electronic structure problem in elemental Pu.

Photoemission and the electronic structure of PuCoGa5.

The electronic structure of the first Pu-based superconductor PuCoGa5 is explored using photoelectron spectroscopy and a novel theoretical scheme. Exceptional agreement between calculation and experiment defines a path forward for understanding the electronic structure aspects of Pu-based materials. The photoemission results show two separate regions of 5f electron spectral intensity, one at the Fermi energy and another centered 1.2 eV below the Fermi level. The results for PuCoGa5 clearly indicate 5f electron behavior on the threshold between localized and itinerant. Comparisons to delta phase Pu metal show a broader framework for understanding the fundamental electronic properties of the Pu 5f levels in general within two configurations, one localized and one itinerant.

Superconductivity caused by the pairing of plutonium 5f Eelectrons in PuCoGa5.

On the basis of electronic structure calculations we identify the superconductivity in the novel, high-temperature superconductor PuCoGa5 to be caused by the pairing of Pu 5f electrons. Assuming delocalized Pu 5f states, we compute theoretical crystallographic constants very near to the experimental ones, and the calculated specific heat coefficient compares reasonably to the measured coefficient. The theoretical Fermi surface is quasi-two-dimensional and the material appears to be close to a magnetic phase instability.

Electronic Structure of δ-Pu and PuCoGa5 from Photoemission and the Mixed Level Model

ABSTRACTThe electronic structure of δ-phase Pu metal and the Pu-based superconductor PuCoGa5 is explored using photoelectron spectroscopy and a novel theoretical scheme. Excellent agreement between calculation and experiment defines a path forward for understanding electronic structure aspects of Pu-based materials. The photoemission results show two separate regions of 5f electron spectral intensity, one at the Fermi energy and another centered 1.2 eV below the Fermi level. A comparison is made between the photoemission data and five computational schemes for δ-Pu. The results for δ-Pu and PuCoGa5 indicate 5f electron behavior on the threshold between localized and itinerant and a broader framework for understanding the fundamental electronic properties of the Pu 5f levels in general within two configurations, one localized and one itinerant.