Magnetic and electrical properties of dhcp NpPd3 and U(1-x)Np(x)Pd3

We have made an extensive study of the magnetic and electrical properties of double-hexagonal closepacked NpPd3 and a range of U(1-x)Np(x)Pd3 compounds with x=0.01, 0.02, 0.05, and 0.50 using magnetization, magnetic susceptibility, electrical resistivity, and heat capacity measurements on polycrystalline samples, performed in the temperature range 2-300 K and in magnetic fields up to 9 T. Two transitions are observed in NpPd3 at T=10 and 30 K. Dilute Np samples (x<0.05) exhibit quadrupolar transitions, with the transition temperatures reduced from those of pure UPd3.Comment: 10 pages, 18 figure

Magnetic Excitations in NpCoGa5

We report the results of inelastic neutron scattering experiments on NpCoGa$_{5}$, an isostructural analogue of the PuCoGa$_{5}$ superconductor. Two energy scales characterize the magnetic response in the antiferromagnetic phase. One is related to a non-dispersive excitation between two crystal field levels. The other at lower energies corresponds to dispersive fluctuations emanating from the magnetic zone center. The fluctuations persist in the paramagnetic phase also, although weaker in intensity. This supports the possibility that magnetic fluctuations are present in PuCoGa$_{5}$, where unconventional d-wave superconductivity is achieved in the absence of magnetic order.Comment: 4 pages, 5 figure

Possible Pairing Mechanisms of PuCoGa5_5 Superconductor

We examine possible pairing mechanisms of superconductivity in PuCoGa$_5$ based on spin-fluctuations or phonons as mediating bosons. We consider experimental data of specific heat C(T) and resistivity $\rho(T)$ as input to determine a consistent scattering boson with the superconducting transition temperature of 18.5K in PuCoGa$_5$. Irrespective to the type of boson, the characteristic boson frequency is found to be $\sim 150 K$ from the resistivity fitting. The spin fluctuation model is most consistent with the experimental resistivity, successfully explaining the anomalous temperature dependence ($\sim \frac{T^2}{150 K +T}$) at low temperatures as well as the saturation behavior at high temperatures. Assuming that the pairing state is non s-wave, the large residual resistivity $\rho_{imp} \sim 20 \mu \Omega cm \sim 120 K$ suggests that an ideally pure sample of PuCoGa$_5$ would have a maximum T$_c$ of 39 K.Comment: 6 pages, 5 figure

Possible mechanism of superconductivity in PuCoGa5 probed by self-irradiation damage

Measurements of the electrical resistivity of a polycrystalline PuCoGa5 sample reveal significant modifications of the superconducting properties as a function of time, due to the increase of defects and impurities resulting from self-irradiation damage. More than four years of aging were necessary to detect a deviation from linearity in the time dependence of the critical temperature. The observed behavior is understood in the framework of the Eliashberg theory, confirming the ¿dirty¿ d-wave character which was already suggested by nuclear magnetic resonance. We show that experimental data accumulated so far can be well reproduced by assuming a phononic mechanism for superconductivity, with reasonable values of the electron-phonon coupling and Coulomb pseudopotential. Further experiments are then required to assess the role of spin fluctuations in stabilizing the superconducting state in this compound.JRC.E.6-Actinides researc

Superconducting gap structure of the 115's revisited

Density functional theory calculations of the electronic structure of Ce- and Pu-based heavy fermion superconductors in the so-called 115 family are performed. The gap equation is used to consider which superconducting order parameters are most favorable assuming a pairing interaction that is peaked at (\pi,\pi,q_z) - the wavevector for the antiferromagnetic ordering found in close proximity. In addition to the commonly accepted $d_{x^2-y^2}$ order parameter, there is evidence that an extended s-wave order parameter with nodes is also plausible. We discuss whether these results are consistent with current observations and possible measurements that could help distinguish between these scenarios.Comment: 8 pages, 4 figures; Accepted for publication in JPC

Nature of non-magnetic strongly-correlated state in delta-plutonium

Ab-initio relativistic dynamical mean-field theory is applied to resolve the long-standing controversy between theory and experiment in the "simple" face-centered cubic phase of plutonium called delta-Pu. In agreement with experiment, neither static nor dynamical magnetic moments are predicted. In addition, the quasiparticle density of states reproduces not only the peak close to the Fermi level, which explains the large coefficient of electronic specific heat, but also main 5f features observed in photoelectron spectroscopy.Comment: 9 pages, 3 figure

Magnetic Properties of NpPdSn

A new compound NpPdSn was prepared and studied by X-ray diffraction, magnetization, heat capacity and electrical resistivity measurements, performed in the temperature range 2-300 K and under magnetic field up to 14 T. The crystal structure determined by single-crystal X-ray analysis is hexagonal with ZrNiAl-type (space group P62m). NpPdSn orders antiferromagnetically at 19 K and exhibits a Curie-Weiss behavior with µ eff = 2.66 µ B and Θ p = −47 K. Bulk properties show temperature variations similar to systems with strong electronic correlations with a large negative paramagnetic Curie temperature and an enhanced low-temperature specific heat (γ ≈ 90 mJ/(mol K 2 )). It suggests that NpPdSn may be classified as a new Np-based antiferromagnetic Kondo lattice, one of the very few known amidst transuranium-based intermetallics

Theory of High-Tc Superconductivity: Accurate Predictions of Tc

The superconducting transition temperatures of high-Tc compounds based on copper, iron, ruthenium and certain organic molecules are discovered to be dependent on bond lengths, ionic valences, and Coulomb coupling between electronic bands in adjacent, spatially separated layers [1]. Optimal transition temperature, denoted as T_c0, is given by the universal expression $k_BT_c0 = e^2 \Lambda / \ell\zeta$; $\ell$ is the spacing between interacting charges within the layers, \zeta is the distance between interacting layers and \Lambda is a universal constant, equal to about twice the reduced electron Compton wavelength (suggesting that Compton scattering plays a role in pairing). Non-optimum compounds in which sample degradation is evident typically exhibit Tc < T_c0. For the 31+ optimum compounds tested, the theoretical and experimental T_c0 agree statistically to within +/- 1.4 K. The elemental high Tc building block comprises two adjacent and spatially separated charge layers; the factor e^2/\zeta arises from Coulomb forces between them. The theoretical charge structure representing a room-temperature superconductor is also presented.Comment: 7 pages 5 references, 6 figures 1 tabl