Joe David Thompson

Recent advances enabled the discovery of heterometallic molecules for many metals: main group, d-block, lanthanides, and some actinides (U, Th). These complexes have at least two different metals joined by bridging ligands or by direct metal-metal bonding interactions. They are attractive because they can enable chemical cooperativity between metals from different parts of the periodic table. Some heterometallics provide access to unique reactivity and others exhibit physical properties that cannot be accessed by homometallic species. We envisioned that transuranic heterometallics might similarly enable new transuranic chemistry, though synthetic routes to such compounds have yet to be developed. Reported here is the first synthesis of a molecular transuranic complex that contains plutonium (Pu) and cobalt (Co). Our analyses of PuCl {CoCp[OP(OEt) ] } showed Pu(iv) and Co(iii) were present and suggested that the Pu(iv) oxidation state was stabilized by the electron donating phosphite ligands. This synthetic method - and the demonstration that Pu(iv) can be stabilized in a heterobimetallic molecular setting - provides a foundation for further exploration of transuranic multimetallic chemistry.

The thermal conductivity of heavy-fermion superconductor CeCoIn_{5} was measured with a magnetic field rotating in the tetragonal a-b plane, with the heat current in the antinodal direction, J|| [100]. We observe a sharp resonance in thermal conductivity for the magnetic field at an angle Θ≈12°, measured from the heat current direction [100]. This resonance corresponds to the reported resonance at an angle Θ^{'}≈33° from the direction of the heat current applied along the nodal direction, J||[110]. Both resonances, therefore, occur when the magnetic field is applied in the same crystallographic orientation in the two experiments, regardless of the direction of the heat current, proving conclusively that these resonances are due to the structure of the Fermi surface of CeCoIn_{5}. We argue that the uncondensed Landau quasiparticles, emerging with field, are responsible for the observed resonance. We support our experimental results with density-functional-theory model calculations of the density of states in a rotating magnetic field. Our calculations, using a model Fermi surface of CeCoIn_{5}, reveal several sharp peaks as a function of the field direction. Our study demonstrates that the thermal-conductivity measurement in rotating magnetic field can probe the normal parts of the Fermi surface deep inside the superconducting state.

Eu 5 In 2 Sb 6 is a member of a family of orthorhombic nonsymmorphic rare-earth intermetallics that combines large localized magnetic moments and itinerant exchange with a low carrier density and perpendicular glide planes. This may result in special topological crystalline (wallpaper fermion) or axion insulating phases. Recent studies of Eu 5 In 2 Sb 6 single crystals have revealed colossal negative magnetoresistance and multiple magnetic phase transitions. Here, we clarify this ordering process using neutron scattering, resonant elastic x-ray scattering, muon spin -rotation, and magnetometry. The nonsymmorphic and multisite character of Eu 5 In 2 Sb 6 results in coplanar noncollinear magnetic structures with an Ising-like net magnetization along the a axis. A reordering transition, attributable to competing ferro- and antiferromagnetic couplings, manifests as the onset of a second commensurate Fourier component. In the absence of spatially resolved probes, the experimental evidence for this low -temperature state can be interpreted either as an unusual double - q structure or in a phase separation scenario. The net magnetization produces variable anisotropic hysteretic effects which also couple to charge transport. The implied potential for functional domain physics and topological transport suggests that this structural family may be a promising platform to implement concepts of topological antiferromagnetic spintronics.

We report a study of the structural, magnetic, transport, and thermodynamic properties of polycrystalline samples of CeRhC2 and LaRhC2. CeRhC2 crystallizes in a tetragonal structure with space group P4(1), and it orders antiferromagnetically below T-N1 approximate to 1.8 K. Powder neutron diffraction measurements reveal a chiral magnetic structure with a single propagation vector Q(m) = (1/2, 1/2, 0.228(5)), indicating an antiferromagnetic arrangement of Ce magnetic moments in the ab plane and incommensurate order along the c axis with a root-mean-square ordered moment of mord = 0.68 mu B. A second antiferromagnetic phase (T-N2) becomes apparent in electrical resistivity, Hall, and heat capacity measurements in fields above 0.3 T. Electrical resistivity measurements reveal that LaRhC2 is a semiconductor with a band gap of E-g similar to 24 meV, whereas resistivity and Hall measurements indicate that CeRhC2 is a semimetal with a carrier concentration of n similar to 1020 cm(-3). With applied hydrostatic pressure, the zero-field antiferromagnetic transition of CeRhC2 is slightly enhanced, and CeRhC2 becomes notably more metallic up to 1.36 GPa. The trend toward metallicity is in line with density-functional calculations that indicate that both LaRhC2 and CeRhC2 are semimetals, but the band overlap is larger for CeRhC2, which has a smaller unit cell volume than that of its La counterpart.