Research ArticleSUPERCONDUCTORS

Real-space localization and quantification of hole distribution in chain-ladder Sr3Ca11Cu24O41 superconductor

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Science Advances  25 Mar 2016:
Vol. 2, no. 3, e1501652
DOI: 10.1126/sciadv.1501652
  • Fig. 1 Crystal structure of SCCO and O-K near-edge structures.

    (A) SCCO structure. (B and C) Annular dark-field (ADF)–STEM images viewed along the [100] (B) and [001] (C) zone axes. Ca and Cu elemental maps (bottom) were obtained using the Ca-L2,3 and Cu-L2,3 edges, respectively. Weighted principal component analysis (PCA) was applied to reduce the noise level. Unlabeled scale bars, 1 nm. (D) O-K edge onset recorded along the [100] and [001] zone axes. H and U indicate the O 2p hole and upper Hubbard band peaks, respectively. The energy resolution was obtained using a monochromator and was comparable to XAS measurements.

  • Fig. 2 Qualitative hole distribution.

    (A and B) ADF-STEM images and O-K edge onset in the [001] (A) and [100] (B) zone axes. The O-K edge onsets highlight intensity variations of the O 2p hole (H) and upper Hubbard (U) bands, whose positions are indicated by red and black arrows, respectively. The ADF-STEM images are represented after alignment (see the Supplementary Materials). Scale bars, 5 Å.

  • Fig. 3 Spectral fitting and quantitative hole distribution.

    (A) SCCO structure in the [001] zone axis. (B) Modeling of the monochromated O-K edge onset in SCCO in the [001] zone axis. (C) Modeling of the spatially resolved O-K edge onset in SCCO corresponding to chains in the [001] zone axis. (D) Same as in (C) for spectra corresponding to ladders. (E to H) Same as in (A) to (D) for the [100] zone axis. Two Gaussian functions were used to model the O 2p hole band (red solid lines) and the upper Hubbard band (UHB) (green solid lines). The edge onset at higher energy (gray solid lines) was modeled using a step function (30). The energy and FWHM of the Gaussian functions were determined from the monochromated spectra in (B) and (F), and only the intensity of the functions was left as free parameters during the fitting process. (I) O 2p hole band and upper Hubbard band fit over a full spectrum image acquired in the [001] zone axis.

  • Fig. 4 Hole distribution within the ladders versus Ca content in Sr14−xCaxCu24O41.

    The hole distribution from this work (red cross) is indicated in comparison with room-temperature data taken from published works [green triangle: optical measurements, Osafune et al. (18); orange star: O 1s XAS, Nücker et al. (6); purple diamond: Hall effect, Tafra et al. (13); black circle: Cu 2p XAS, Huang et al. (9); blue square: O 1s XAS, Rusydi et al. (7); dark cyan square: 63Cu and 17O NMR, Piskunov et al. (11); gray hexagon: neutron diffraction, Deng et al. (17)].

  • Table 1 Hole concentrations (per f.u.) in chains and ladders.

    The error bars correspond to the SD over all data sets analyzed and adjustment of the absolute energy positions of the O 2p hole band and the upper Hubbard band.

    LaddersChains
    [100]1.99 ± 0.284.01 ± 0.28
    [001]1.92 ± 0.264.08 ± 0.26
  • Table 2 Calculated contributions of chains and ladders to the total inelastic intensity.
    OrientationBeam positionInelastic intensity from ladders (a.u.)Inelastic intensity from chains (a.u.)
    [100]Ladders155,956 (~84%)28,902 (~16%)
    Chains17,683 (~7%)240,596 (~93%)
    [001]Ladders139,527 (~84%)26,567 (~16%)
    Chains35,524 (~17%)177,920 (~83%)

Supplementary Materials

  • Supplementary material for this article is available at http://advances.sciencemag.org/cgi/content/full/2/3/e1501652/DC1

    Comparison with x-ray absorption spectroscopy

    Quantitative evaluation of the hole distribution

    Inelastic scattering calculations

    Drift correction

    Qualitative hole distribution from Cu 2p excitation

    Table S1. Fitting parameters: SD and relative energy positions of Gaussian functions.

    Fig. S1. Comparison of O-K XANES and ELNES.

    Fig. S2. Inelastic channeling calculations.

    Fig. S3. Spatial drift correction on the STEM-EELS data.

    Fig. S4. Qualitative hole distribution from Cu 2p excitation.

  • Supplementary Materials

    This PDF file includes:

    • Comparison with x-ray absorption spectroscopy
    • Quantitative evaluation of the hole distribution
    • Inelastic scattering calculations
    • Drift correction
    • Qualitative hole distribution from Cu 2p excitation
    • Table S1. Fitting parameters: SD and relative energy positions of Gaussian
      functions.
    • Fig. S1. Comparison of O-K XANES and ELNES.
    • Fig. S2. Inelastic channeling calculations.
    • Fig. S3. Spatial drift correction on the STEM-EELS data.
    • Fig. S4. Qualitative hole distribution from Cu 2p excitation.

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