Competition between Covalent Bonding and Charge Transfer at Complex-Oxide Interfaces

Juan Salafranca, Julián Rincón, Javier Tornos, Carlos León, Jacobo Santamaria, Elbio Dagotto, Stephen J. Pennycook, and Maria Varela

Phys. Rev. Lett. 112, 196802 – Published 14 May 2014; Erratum Phys. Rev. Lett. 113, 189902 (2014)

Abstract

Here we study the electronic properties of cuprate-manganite interfaces. By means of atomic resolution electron microscopy and spectroscopy, we produce a subnanometer scale map of the transition metal oxidation state profile across the interface between the high Tc superconductor ${YBa}_{2} {Cu}_{3} O_{7 - δ}$ and the colossal magnetoresistance compound (La,Ca) ${MnO}_{3}$ . A net transfer of electrons from manganite to cuprate with a peculiar nonmonotonic charge profile is observed. Model calculations rationalize the profile in terms of the competition between standard charge transfer tendencies (due to band mismatch), strong chemical bonding effects across the interface, and Cu substitution into the Mn lattice, with different characteristic length scales.

Received 20 October 2013

DOI:https://doi.org/10.1103/PhysRevLett.112.196802

Erratum

Erratum: Competition between Covalent Bonding and Charge Transfer at Complex-Oxide Interfaces [Phys. Rev. Lett. 112, 196802 (2014)]

Juan Salafranca, Julián Rincón, Javier Tornos, Carlos León, Jacobo Santamaria, Elbio Dagotto, Stephen J. Pennycook, and Maria Varela

Phys. Rev. Lett. 113, 189902 (2014)

Authors & Affiliations

Juan Salafranca^1,2,*, Julián Rincón^2,3, Javier Tornos¹, Carlos León¹, Jacobo Santamaria¹, Elbio Dagotto^2,4, Stephen J. Pennycook⁵, and Maria Varela^2,1

¹Grupo de Física de Materiales Complejos, Universidad Complutense, 28040 Madrid, Spain
²Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, USA
³Center for Nanophase Materials Sciences, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, USA
⁴Department of Physics and Astronomy, The University of Tennessee, Knoxville, Tennessee 37996, USA
⁵Department of Materials Science and Engineering, The University of Tennessee, Knoxville, Tennessee 37996, USA

^*Corresponding author. jsalafra@ucm.es

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Issue

Vol. 112, Iss. 19 — 16 May 2014

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Images

Figure 1
(a) High-resolution, $Z$ -contrast image of a LCMO/YBCO/LCMO trilayer. (b) Map of transition metal spacings, $Δ z$ , along the c direction, with a lateral average of the image (right). ${CuO}_{2}$ biplanes are characterized by a smaller distance (dark stripes). (c) RGB compound image (left) and EELS maps of the integrated intensity of $O K$ edge, Mn $L_{2, 3}$ , Ba $M_{4, 5}$ and $La M_{4, 5}$ edges, as labeled. The RGB imaged is obtained by overlaying the Mn (red), La (green) and Ba (blue) maps. The right panel shows the normalized integrated intensities of the Mn $L_{2, 3}$ (red), Ba $M_{4, 5}$ (blue), and La $M_{4, 5}$ (green) across a LCMO(top)/YBCO(bottom) interface, extracted from an EELS line scan. An orange rectangle marks the width of a perovskite unit cell block at the interface.
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Figure 2
(a) $Z$ -contrast image of a LCMO/YBCO multilayer on a (100) ${SrTiO}_{3}$ substrate. Arrows mark LCMO (red) and YBCO layers (blue). The inset shows an EELS line-scan acquired along the growth direction. The right panel shows the energy range corresponding to the $O K$ edge across one of the YBCO-LCMO interfaces in the line scan. Dashed lines marked the position of the O prepeak for LCMO and YBCO away from the interface. (b) Prepeak intensity (top), and the edge onset position (bottom) along the growth direction, marked with a light blue arrow. Some data adapted from previous work (see Supplemental Material [33] for details).
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Figure 3
Experimental and theoretical charge profiles. (a) Experimental charge profiles across the LCMO layer in multilayers with different thicknesses $Z_{LCMO}$ . Some data adapted from previous work (see Supplemental Material [33] for details). (b) Results of the model calculations, including (empty symbols) and excluding (full) the polar discontinuity at the interface. Blue symbols correspond to YBCO and red symbols correspond to LCMO. Notice that polar discontinuity cannot account for the electron enrichment at LCMO near the interface. (c) Effect of oxygen vacancies. $δ$ labels the oxygen deficiency in the Mn plane closest to the interface (of chemical formula ${MnO}_{2 - δ}$ ). Although oxygen vacancies dope the interface with electrons, the charge profiles in the LCMO layer decrease monotonically to zero, unlike the experiments in (a). (d) Effect of strong hybridization of Cu and Mn orbitals in the model and of hybridization together with Cu substitution in LCMO first atomic plane (as indicated), showing the nonmonotonic charge profile as in (a). (e) Effect of Hubbard $U$ interaction, showing a charge-transfer scenario for $U \leq t_{0}$ . Details about the model in the main text and Supplemental Material [33].
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