Quantum phase transition in quasi-one-dimensional BaRu6O12

Evidence of electron correlation and weak bulk plasmon in SrMoO3

We investigate the electronic structure of highly conducting perovskite SrMoO₃using valence band photoemission spectroscopy and electronic structure calculations. Large intensity corresponding to coherent feature close to Fermi level is captured by density functional theory (DFT) calculation. An additional satellite at ∼3 eV binding energy remains absent in DFT, hybrid functional (DFT-hybrid) and dynamical mean field theory (DFT + DMFT) calculations. Mo 4dspectra obtained with different surface sensitive photoemission spectroscopy suggest different surface and bulk electronic structures. DFT + DMFT spectral function is in excellent agreement with the coherent feature in the bulk Mo 4dspectra, revealing moderate electron correlation strength. A large plasmon satellite and signature of strong electron correlation are observed in the surface spectra, while the bulk spectra exhibits aweakplasmon satellite.

Anisotropic Electrical Conductivity of Oxygen-Deficient Tungsten Oxide Films with Epitaxially Stabilized 1D Atomic Defect Tunnels

Materials having an anisotropic crystal structure often exhibit anisotropy in the electrical conductivity. Compared to complex transition-metal oxides (TMOs), simple TMOs rarely show large anisotropic electrical conductivity due to their simple crystal structure. Here, we focus on the anisotropy in the electrical conductivity of a simple TMO, oxygen-deficient tungsten oxide (WO_x) with an anisotropic crystal structure. We fabricated several WO_x films by the pulsed laser deposition technique on the lattice-matched (110)-oriented LaAlO₃ substrate under a controlled oxygen atmosphere. The crystallographic analyses of the WO_x films revealed that highly dense atomic defect tunnels were aligned one-dimensionally (1D) along [001] LaAlO₃. The electrical conductivity along the 1D atomic defect tunnels was ∼5 times larger than that across the tunnels. The present approach, introduction of 1D atomic defect tunnels, might be useful to design simple TMOs exhibiting anisotropic electrical conductivity.

Extreme thermopower anisotropy and interchain transport in the quasi-one-dimensional metal Li0.9Mo6O17

Thermopower and electrical resistivity measurements transverse to the conducting chains of the quasi-one-dimensional metal Li0.9Mo6O17 are reported in the temperature range 5≤T≤500  K. For T≥400  K the interchain transport is determined by thermal excitation of charge carriers from a valence band ∼0.14  eV below the Fermi level, giving rise to a large, p-type thermopower that coincides with a small, n-type thermopower along the chains. This dichotomy-semiconductorlike in one direction and metallic in a mutually perpendicular direction-gives rise to substantial transverse thermoelectric effects and a transverse thermoelectric figure of merit among the largest known for a single compound.

Evolution of electronic and magnetic properties in four polytypes of BaRuO3: a first-principles study

Using density functional theory, we explore the evolution of the electronic and magnetic properties of BaRuO3 in four different phases, 9R, 4H, 6H and 3C, obtained by synthesizing under different pressure conditions. The four different phases differ in the differential proportion of hexagonal versus cubic close stacking of the BaO3 layers, leading to important changes in the structure. By computing the electronic and magnetic properties of the four different phases, and the optical properties of 4H and 9R phases, we find that density functional based calculations are to a large extent able to explain the change in properties of the four different polytypes.

Spin-lozenge thermodynamics and magnetic excitations in Na(3)RuO(4)

We report inelastic and elastic neutron scattering, magnetic susceptibility, and heat capacity measurements for polycrystalline sodium ruthenate (Na(3)RuO(4)). Previous work suggests that this material consists of isolated tetramers of S = 3/2  Ru(5+) ions in a so-called lozenge configuration. Comparisons of magnetic susceptibility and inelastic and elastic neutron scattering results with analytic calculations for several cluster models show that although there may be significant spin-spin correlations within the lozenge cluster, a simple isolated lozenge model is not appropriate for Na(3)RuO(4).

High-pressure synthesis of the cubic perovskite BaRuO3 and evolution of ferromagnetism in ARuO3 (A = Ca, Sr, Ba) ruthenates

The cubic perovskite BaRuO(3) has been synthesized under 18 GPa at 1,000 degrees C. Rietveld refinement indicates that the new compound has a stretched Ru-O bond. The cubic perovskite BaRuO(3) remains metallic to 4 K and exhibits a ferromagnetic transition at T(c) = 60 K, which is significantly lower than the T(c) approximately = 160 K for SrRuO(3). The availability of cubic perovskite BaRuO(3) not only makes it possible to map out the evolution of magnetism in the whole series of ARuO(3) (A = Ca, Sr, Ba) as a function of the ionic size of the A-site r(A,) but also completes the polytypes of BaRuO(3). Extension of the plot of T(c) versus r(A) in perovskites ARuO(3) (A = Ca, Sr, Ba) shows that T(c) does not increase as the cubic structure is approached, but has a maximum for orthorhombic SrRuO(3). Suppressing T(c) by Ca and Ba doping in SrRuO(3) is distinguished by sharply different magnetic susceptibilities chi(T) of the paramagnetic phase. This distinction has been interpreted in the context of a Griffiths' phase on the (Ca Sr)RuO(3) side and bandwidth broadening on the (Sr,Ba)RuO(3) side.

NaV2O4: a quasi-1D metallic antiferromagnet with half-metallic chains

NaV2O4 crystals were grown under high pressure using a NaCl flux, and the crystals were characterized with x-ray diffraction, electrical resistivity, heat capacity, and magnetization. The structure of NaV2O4 consists of double chains of edge-sharing VO6 octahedra. The resistivity is highly anisotropic, with the resistivity perpendicular to the chains more than 20 times greater than that parallel to the chains. Magnetically, the intrachain interactions are ferromagnetic and the interchain interactions are antiferromagnetic; 3D antiferromagnetic order is established at 140 K. First-principles electronic structure calculations indicate that the chains are half-metallic. Interestingly, the case of NaV2O4 seems to be a quasi-1D analogue of what was found for half-metallic materials.

Metallic ground state and glassy transport in single crystalline URh2Ge2: enhancement of disorder effects in a strongly correlated electron system

We present a detailed study of the electronic transport properties on a single crystalline specimen of the moderately disordered heavy-fermion system URh2Ge2. For this material, we find glassy electronic transport in a single crystalline compound. We derive the temperature dependence of the electrical conductivity and establish metallicity by means of optical conductivity and Hall effect measurements. The overall behavior of the electronic transport properties closely resembles that of metallic glasses, with at low temperatures an additional minor spin disorder contribution. We argue that this glassy electronic behavior in a crystalline compound reflects the enhancement of disorder effects as a consequence of strong electronic correlations.