Research ArticleMATERIALS SCIENCE

Nearly free electrons in a 5d delafossite oxide metal

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Science Advances  23 Oct 2015:
Vol. 1, no. 9, e1500692
DOI: 10.1126/sciadv.1500692
  • Fig. 1 Single-crystal PtCoO2 samples.

    (A) Optical microscope image of as-grown crystals of PtCoO2. (B) Le Bail fitting of powder XRD pattern along with the fitted and the difference curve. All peaks are labeled with corresponding hkl values. Peaks marked with “*” correspond to unavoidable unreacted PtCl2 stuck to the crystal surface. (C) SEM image of a sample used for transport measurements in which a focused ion beam was used to define a measurement track of well-defined geometry.

  • Fig. 2 Temperature-dependent transport.

    (A) The temperature-dependent in-plane resistivity of PtCoO2 in zero applied magnetic field. The inset shows a magnified view of the low-temperature resistivity, revealing an upturn below 16 K. (B) Temperature dependence of the Hall coefficient (RH), calculated by taking the field gradient between 7 and 9 T of the data shown in fig. S1.

  • Fig. 3 Single-band faceted Fermi surface.

    (A) Fermi surface of PtCoO2 measured by ARPES integrated over EF ± 5 meV. The solid line represents the Brillouin zone. (B) The Fermi surface area is 8% smaller than would be expected for a half-filled band, as discussed in the main text, but its shape is in agreement with the Fermi surface obtained from GGA (general gradient approximation) + SO (spin orbit) + U calculations (U = 4 eV), shown in red and scaled to match the experimental area. The dots represent the Fermi momenta extracted from (A) by radially fitting momentum distribution curves (MDCs) around the measured Fermi surface.

  • Fig. 4 Electronic structure.

    (A) Calculated bulk electronic structure (see Materials and Methods) with and without SOC. The high-symmetry points are labeled on the bulk Brillouin zone (inset). Inclusion of SOC pushes the hole bands at, for example, the L-point below EF while leaving the remaining bands crossing the Fermi level almost unchanged. (B and C) Partial (B) and orbitally resolved (C) density of states (DOS) (including SOC), revealing the states at EF to originate almost exclusively from Pt 5d.

  • Fig. 5 Weakly interacting quasiparticle dispersion.

    (A) Electronic structure along the Γ − K direction. The single band crossing the Fermi level can be traced down to more 0.5 eV binding energy with little broadening. The dashed red line corresponds to a parabolic dispersion with an effective mass m* = 1.09me. An MDC at the Fermi level (EF ± 6 meV) is shown by the dots, with a fit to a Lorentzian peak indicating a full width at half maximum of 0.04 Å–1. (B) The gray and black dots represent the peak positions of the fits to the MDCs along the Γ − M and Γ − K direction, respectively. A linear fit to each data set independently yields a Fermi velocity of 8.9 × 105 m/s (shown by the solid line), giving an effective mass of 1.09me along Γ − K and 1.27me along Γ − M.

Supplementary Materials

  • Supplementary Materials

    This PDF file includes:

    • Hall effect measurement
    • Fig. S1. Field-dependent Hall effect measurements.
    • Calculated density of states
    • Fig. S2. Additional density-of-states calculations.
    • Reference (49)

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