Electronic correlations in FeGa3 and the effect of hole doping on its magnetic properties

We investigate signatures of electronic correlations in the narrow-gap semiconductor FeGa 3 by means of electrical resistivity and thermodynamic measurements performed on single crystals of FeGa 3 , Fe 1−x Mn x Ga 3 , and FeGa 3−y Zn y , complemented by a study of the 4d analog material RuGa 3 . We find that the inclusion of sizable amounts of Mn and Zn dopants into FeGa 3 does not induce an insulator-to-metal transition. Our study indicates that both substitution of Zn onto the Ga site and replacement of Fe by Mn introduces states into the semiconducting gap that remain localized even at highest doping levels. Most importantly, using neutron powder diffraction measurements, we establish that FeGa 3 orders magnetically above room temperature in a complex structure, which is almost unaffected by the doping with Mn and Zn. Using realistic many-body calculations within the framework of dynamical mean field theory (DMFT), we argue that while the iron atoms in FeGa 3 are dominantly in an S=1 state, there are strong charge and spin fluctuations on short-time scales, which are independent of temperature. Further, the low magnitude of local contributions to the spin susceptibility advocates an itinerant mechanism for the spin response in FeGa 3 . Our joint experimental and theoretical investigations classify FeGa 3 as a correlated band insulator with only small dynamical correlation effects, in which nonlocal exchange interactions are responsible for the spin gap of 0.4 eV and the antiferromagnetic order. We show that hole doping of FeGa 3 leads, within DMFT, to a notable strengthening of many-body renormalizations

Magnetic structure of Yb2Pt2Pb: Ising moments on the Shastry-Sutherland lattice.

Neutron diffraction measurements were carried out on single crystals and powders of Yb2Pt2Pb, where Yb moments form two interpenetrating planar sublattices of orthogonal dimers, a geometry known as Shastry-Sutherland lattice, and are stacked along the c axis in a ladder geometry. Yb2Pt2Pb orders antiferromagnetically at TN=2.07K, and the magnetic structure determined from these measurements features the interleaving of two orthogonal sublattices into a 5×5×1 magnetic supercell that is based on stripes with moments perpendicular to the dimer bonds, which are along (110) and (−110). Magnetic fields applied along (110) or (−110) suppress the antiferromagnetic peaks from an individual sublattice, but leave the orthogonal sublattice unaffected, evidence for the Ising character of the Yb moments in Yb2Pt2Pb that is supported by point charge calculations. Specific heat, magnetic susceptibility, and electrical resistivity measurements concur with neutron elastic scattering results that the longitudinal critical fluctuations are gapped with ΔE≃0.07meV

Coexistence of magnetic order and valence fluctuations in the Kondo lattice system Ce2Rh3Sn5

We report on the electronic band structure, structural, magnetic, and thermal properties of Ce2Rh3Sn5. Ce LIII-edge XAS spectra give direct evidence for an intermediate valence behavior. Thermodynamic measurements reveal magnetic transitions at TN1≈2.9 K and TN2≈2.4 K. Electrical resistivity shows behavior typical for the Kondo lattices. The coexistence of magnetic order and valence fluctuations in a Kondo lattice system we attribute to a peculiar crystal structure in which Ce ions occupy two distinct lattice sites. Analysis of the structural features of Ce2Rh3Sn5, together with results of electronic band structure calculations and thermodynamic and spectroscopic data indicate that at low temperatures only Ce ions from the Ce1 sublattice adopt a stable trivalent electronic configuration and show local magnetic moments that give rise to the magnetic ordering. By contrast, our study suggests that Ce2 ions exhibit a nonmagnetic Kondo-singlet ground state. Furthermore, the valence of Ce2 ions estimated from the Ce LIII-edge XAS spectra varies between +3.18 at 6 K and +3.08 at room temperature. Thus our joined experimental and theoretical investigations classify Ce2Rh3Sn5 as a multivalent charge-ordered system

Electronic structure of CeRhX (X=Sn, In)

79.60.-i Photoemission and photoelectron spectra, 71.20.LP Intermetallic compounds, 71.27.+a Strongly correlated electron systems; heavy fermions,

Electronic structure of Ce 5 Rh 4 Sn 10 from XPS and band structure calculations

We present a combined experimental and theoretical study of the electronic structure for the heavy-fermion antiferromagnet Ce 5Rh 4Sn 10 based on X-ray photoemission spectroscopy (XPS) data and ab initio band structure calculations. The Ce core-level XPS spectra point to a stable trivalent configuration of Ce atoms in Ce 5Rh 4Sn 10 , consistently with both the magnetic susceptibility data and the results of computational structure optimization. The band structure calculations confirm a magnetic ground state with significant magnetic moments only at the Ce atoms. The qualitatively correct description of Ce 3+ in Ce 5Rh 4Sn 10 has been achieved using the LSDA+U approach for the Ce 4f states. The comparison of the theoretical results with experimental XPS valence band spectrum supports their validity. The calculated partial densities of states suggest that there is a variation in binding energy of the occupied 4f states between Ce atoms in nonequivalent crystallographic positions, which is related to the hybridization with Sn states. Finally, the band structure and charge density maps point to the formation of zig-zag chains of the strongly bounded Sn(2), Sn(3) and Rh atoms along the tetragonal axis, whereas Sn(1) shows nearly dispersionless 5s bands. Copyright EDP Sciences/Società Italiana di Fisica/Springer-Verlag 200879.60.-i Photoemission and photoelectron spectra, 71.20.Lp Intermetallic compounds, 71.27.+a Strongly correlated electron systems; heavy fermions,

Electronic structure and thermodynamic properties of Ce3Rh4Sn13 and La3Rh4Sn13

We report on the electronic structure and basic thermodynamic properties of Ce3Rh4Sn13 and of the reference compound La3Rh4Sn13. XPS core-level spectra revealed a stable trivalent configuration of the Ce atoms in Ce3Rh4Sn13, consistent with magnetic susceptibility data. Band structure calculations within the LSDA+U approximation yield the qualitatively correct description of Ce in a trivalent state. The reliability of the theoretical results has been confirmed by a comparison of the calculated XPS valence band spectra with experimental data. The calculated densities of states as well as the rare-earth (RE) 3d XPS spectra point to a weak hybridization between the RE 4f shell and the conduction band states. The band structure calculations result in a magnetic ground state for Ce3Rh4Sn13. Previous analysis pointed to the partial occupancy of the 2a site by Sn atoms. The charge density analysis reveals the dominant metallic character of the chemical bonding at the 2a atomic position. Simulation of vacancies at the 2a site using the virtual crystal approximation (VCA) indicate that the magnetic properties of Ce3Rh4Sn13 strongly depend on the Sn content, which could explain the discrepancy in magnetic properties between different Ce3Rh4Sn13 samples

Combining a parsimonious mathematical model with infection data from tailor-made experiments to understand environmental transmission

Abstract Although most infections are transmitted through the environment, the processes underlying the environmental stage of transmission are still poorly understood for most systems. Improved understanding of the environmental transmission dynamics is important for effective non-pharmaceutical intervention strategies. To study the mechanisms underlying environmental transmission we formulated a parsimonious modelling framework including hypothesised mechanisms of pathogen dispersion and decay. To calibrate and validate the model, we conducted a series of experiments studying distance-dependent transmission of Campylobacter jejuni in broilers. We obtained informative simultaneous estimates for all three model parameters: the parameter of C. jejuni inactivation, the diffusion coefficient describing pathogen dispersion, and the transmission rate parameter. The time and distance dependence of transmission in the fitted model is quantitatively consistent with marked spatiotemporal patterns in the experimental observations. These results, for C. jejuni in broilers, show that the application of our modelling framework to suitable transmission data can provide mechanistic insight in environmental pathogen transmission

Research data supporting "Large Fermi Surface of Heavy Electrons at the Border of Mott Insulating State in NiS2"

High pressure, low temperature, high magnetic field data obtained on high quality single crystals of NiS2, to clarify the nature of the pressure induced metal-insulator transition and to map out key parts of the electronic Fermi surface in the high pressure metallic state. Resistivity measurements under pressure were carried out at the Cavendish Laboratory, Cambridge, and tank circuit oscillator measurements were carried out at NHMFL Tallahassee. The Fermi surface calculations were performed using Wien2k and plotted using Xcrysden. Details of the methods and analysis methods are published in the Scientific Reports article with the same name.This work was supported by the ERC, EPSRC [grant number EP/K012894/1], NSF [grant number DMR-1157490], DOE [grant number NNSA SSAA DE-NA0001979]