Long-Range Incommensurate Charge Fluctuations in (Y,Nd)Ba2Cu3O6+x

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Science  17 Aug 2012:
Vol. 337, Issue 6096, pp. 821-825
DOI: 10.1126/science.1223532
  • Fig. 1

    Resonant soft x-ray scattering from layered cuprates. (A) Crystalline structure of YBa2Cu3O6+x superconductors. For x < 1, some of the O atoms along the chains are missing. (B) Scattering geometry with the c and either a or b axes in the scattering plane. The incident photon polarization can be parallel (π) or perpendicular (σ) to the scattering plane. The real and reciprocal spaces are sketched in the front and rear plane, respectively. In the real-space image, the Cu 3dx2y2 and O 2p orbitals are shown. In the reciprocal-space image, the nuclear and magnetic first Brillouin zones are drawn with solid and dotted lines, respectively; the thick green line indicates the range covered by the experiments. Γ labels the (0,0) point, origin of the reciprocal space and center of the first Brillouin zone. (C) The in-plane component q// of the transferred momentum ranges from –0.4 to +0.4 rlu along the (1,0) or (0,1) direction when the sample is rotated around the y axis at a fixed scattering angle, indicated by the gray arcs (130° in most cases). (D) In the Cu L3 energy-resolved RXS spectra of underdoped Nd1.2Ba1.8Cu3O7 (Tc = 65 K, T = 15 K, σ polarization), the quasi-elastic component has a maximum intensity at q// = −0.31 rlu. The dispersing paramagnons (spin) are visible next to the quasi-elastic peak; the interorbital excitations (dd) around 2 eV carry most of the spectral weight.

  • Fig. 2

    Polarization and energy dependence of the REXS peak in YBa2Cu3O6.6. (A) REXS scans measured at the Cu L3 edge for positive and negative values of q// along (1,0) and (0,1), using σ polarization (20). (B) Ratio between the REXS signal intensities obtained with π and σ polarizations (pol.). The experimental data for YBa2Cu3O6.6 and Nd1.2Ba1.8Cu3O7 are compared to the model calculations (see text for details) and to the magnetic excitation signal (100- to 300-meV energy loss). (C) XAS spectra of YBa2Cu3O6.6 with two polarizations and two geometries corresponding to negative and positive values of q// (Fig. 1C). The main contributions to the XAS peaks are indicated. RXS with photon energies at the main absorption peak of 931.5 eV selects signals arising from the Cu2 sites. (D and E) REXS scans show the CDW peak only when exciting at the Cu2 sites and show nothing at higher excitation energies.

  • Fig. 3

    Dependence of the CDW signal at 15 K on the hole doping level p. The CDW signal is present in several YBa2Cu3O6+x and Nd1+yBa2−yCu3O7 samples, but only for 0.09 ≤ p ≤ 0.13. In this doping range (shaded in the central panel), the Tc-versus-p relation exhibits a plateau. The CDW peak position does not change with p outside of the experimental error, but its intensity is maximum at Embedded Image.

  • Fig. 4

    Temperature dependence of the CDW signal in YBa2Cu3O6.6. (A and B) Comparison of RXS scans at selected temperatures, as obtained with an energy-resolving instrument and with a conventional diffractometer for soft x-rays. (C and D) T-dependence of the CDW intensity and full width at half maximum (FWHM) derived from the energy-resolved (open circles) and the energy-integrated data (solid circles) for σ polarization.

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  • Long-Range Incommensurate Charge Fluctuations in (Y,Nd)Ba2Cu3O6+x

    G. Ghiringhelli, M. Le Tacon, M. Minola, S. Blanco-Canosa, C. Mazzoli, N. B. Brookes, G. M. De Luca, A. Frano, D. G. Hawthorn, F. He, T. Loew, M. Moretti Sala, D. C. Peets, M. Salluzzo, E. Schierle, R. Sutarto, G. A. Sawatzky, E. Weschke, B. Keimer, L. Braicovich

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    • Materials and Methods
    • Figs. S1 to S4
    • Table S1
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    Revised 15 August 2012: The full reference list and in-text citations have been updated in this version of the supplementary materials.
    The original version is still available here.

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