Resolving CuO chain and ${\mathrm{CuO}}_{2}$ plane contributions to the ${\mathrm{YBa}}_{2}{\mathrm{Cu}}_{3}{\mathrm{O}}_{7\ensuremath{-}\ensuremath{\delta}}$ valence band by standing-wave excited hard x-ray photoelectron spectroscopy

Resolving CuO chain and ${CuO}_{2}$ plane contributions to the ${YBa}_{2} {Cu}_{3} O_{7 - δ}$ valence band by standing-wave excited hard x-ray photoelectron spectroscopy

S. Thiess, T.-L. Lee, C. Aruta, C. T. Lin, F. Venturini, N. B. Brookes, B. C. C. Cowie, and J. Zegenhagen

Phys. Rev. B 92, 075117 – Published 10 August 2015

Abstract

We analyzed the valence band (VB) of the 90 K high-temperature superconductor ${YBa}_{2} {Cu}_{3} O_{7 - δ}$ by photoelectron spectroscopy under standing-wave excitation employing hard x rays. Precisely positioning the standing-wave intensity in the unit cell allows selectively probing the VB yield from the CuO chains and ${CuO}_{2}$ planes, respectively. Both contribute strongly over the whole VB but the spectral weight of the planes is significantly higher than the chains within about 2 eV from the Fermi level. In the x-ray regime, the major contribution to the VB emission is coming from Cu $3 d$ .

Received 23 October 2014
Revised 14 May 2015

DOI:https://doi.org/10.1103/PhysRevB.92.075117

Physics Subject Headings (PhySH)

Density of states

High-temperature superconductors

Hard x-ray photoelectron spectroscopy X-ray standing waves

Condensed Matter, Materials & Applied Physics

Authors & Affiliations

S. Thiess^1,*, T.-L. Lee^1,†, C. Aruta², C. T. Lin³, F. Venturini^1,†, N. B. Brookes¹, B. C. C. Cowie^1,‡, and J. Zegenhagen^1,§

¹European Synchrotron Radiation Facility (ESRF), 71 Avenue des Martyrs, 38043 Grenoble, France
²CNR-SPIN, Via del Politecnico 1, 00133 Roma, Italy
³Max-Planck-Institut für Festkörperforschung, Heisenbergstrasse 1, 70569 Stuttgart, Germany

^*Present address: DESY, Notkestrasse 85, 22607 Hamburg, Germany.
^†Present address: Diamond Light Source Ltd., Harwell Science and Innovation Campus, Didcot OX11 0DE, UK.
^‡Present address: Australian Synchrotron Company Ltd., 800 Blackburn Road, Clayton, VIC 3168, Australia.
^§Present address: Diamond Light Source Ltd., Harwell Science and Innovation Campus, Didcot OX11 0DE, UK; jorg.zegenhagen@diamond.ac.uk

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Vol. 92, Iss. 7 — 15 August 2015

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Figure 1
(a) Structure of ${YBa}_{2} {Cu}_{3} O_{7}$ , space group $P m m m$ , lattice parameter $c = 1.168$ nm. The fourfold oxygen coordination of the chain Cu(1) sites and the in-plane Cu(2) sites is shown shaded. (b) Calculated pDOS at the Cu(1) and Cu(2) sites adapted from Larbaoui et al. [17]. Dotted lines: pDOS broadened by 0.75 eV to account for the experimental resolution.
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Figure 2
Photoelectron core level spectra from a low-temperature cleaved ${YBa}_{2} {Cu}_{3} O_{7 - δ}$ single crystal with 3.73 keV excitation energy.
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Figure 3
Core and valence level XSW yield for YBCO( $00 ℓ$ ) reflections at energies $E_{γ}$ around Bragg energies $E_{B r}$ of 2.661, 3.193, and 3.725 keV for $ℓ = 5$ , 6, and 7, respectively. Corresponding rocking curves are shown on the bottom of the plots. Symbols represent the Shirley background subtracted peak integral of the corresponding electronic levels recorded in constant initial state mode at the specific $E_{γ}$ and lines are fits to the data based on the DTXD [11] according to standard XSW procedure [6, 28]. The movement of the wave field (spacing of $c / ℓ$ ) through the YBCO unit cell along the $c$ axis causes strong modulation of the electron yields. The curves for the individual electronic levels, as labeled on the right-hand side, are offset for clarity. Error bars are about the size of the symbols or smaller.
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Figure 4
XSW results employing the YBCO(007) reflection. VB yield curves (left diagram) recorded at four different positions on the YBCO(007) rocking curve (right-hand diagram). Wave-field maxima are on the Cu(1) and Cu(2) site at a and d, respectively. VB spectra: Symbols are data and lines are guides to the eye; the curves are normalized and offset on the vertical scale for clarity. The inset shows the indicated top part of curve a (dashed) and d (solid line) without offset on an enlarged scale with the size of the error bars indicated. YBCO(007) rocking curve: Symbols are data and line is fit to the data with the help of DTXD.
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Figure 5
XSW analysis of the contributions of Cu(1) (chains) and Cu(2) (planes) to the YBCO VB emission determined from the XSW data recorded for the YBCO(007) reflection shown in Fig. 4 (upper diagram) compared with the calculated pDOS from Fig. 1 (lower diagram) broadened by 1.2 eV, which is 50% larger than the instrumental resolution of 0.75 eV. In a heuristic approach, both diagrams are shifted relative to each other to better align the weight of the spectra.
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Physical Review B

covering condensed matter and materials physics

Resolving CuO chain and ${CuO}_{2}$ plane contributions to the ${YBa}_{2} {Cu}_{3} O_{7 - δ}$ valence band by standing-wave excited hard x-ray photoelectron spectroscopy

S. Thiess, T.-L. Lee, C. Aruta, C. T. Lin, F. Venturini, N. B. Brookes, B. C. C. Cowie, and J. Zegenhagen

Phys. Rev. B 92, 075117 – Published 10 August 2015

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Physical Review B

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Resolving CuO chain and CuO2 plane contributions to the YBa2Cu3O7−δ valence band by standing-wave excited hard x-ray photoelectron spectroscopy

S. Thiess, T.-L. Lee, C. Aruta, C. T. Lin, F. Venturini, N. B. Brookes, B. C. C. Cowie, and J. Zegenhagen

Phys. Rev. B 92, 075117 – Published 10 August 2015

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Resolving CuO chain and ${CuO}_{2}$ plane contributions to the ${YBa}_{2} {Cu}_{3} O_{7 - δ}$ valence band by standing-wave excited hard x-ray photoelectron spectroscopy