Direct Evidence of the Competing Nature between Electronic and Lattice Breathing Order in Rare-Earth Nickelates

Jong-Woo Kim, Yongseong Choi, S. Middey, D. Meyers, J. Chakhalian, Padraic Shafer, H. Park, and Philip J. Ryan

Phys. Rev. Lett. 124, 127601 – Published 26 March 2020

Abstract

Correlated electrons give rise to both exotic electronic and magnetic properties in rare-earth nickelates. Here we present evidence of the interfacial coupling between two nickelate systems, ${EuNiO}_{3}$ (ENO) and ${LaNiO}_{3}$ (LNO), with different electronic and magnetic properties but with compatible structural registry giving rise to an electrostructural transition, unobserved in each constituent. Nominally, LNO remains in a paramagnetic-metallic $R \bar{3} c$ phase while orthorhombic ENO undergoes antiferromagnetic and insulating transitions. However, the ENO/LNO heterostructure displays a uniform rotational symmetry set by an entwined interface. This leads to an anomalous reduction of bond disproportionation in the ENO layer through the metal to insulator transition and concomitantly charge disproportionation opens the gap accompanied by antiferromagnetic ordering. Our results resolve a long-standing question in the physics of rare-earth nickelates, herein demonstrating that charge and bond disproportionation are competing mechanisms for the charge localization process in the rare-earth nickelate system.

Received 26 June 2019
Accepted 6 February 2020

DOI:https://doi.org/10.1103/PhysRevLett.124.127601

Physics Subject Headings (PhySH)

Electronic structure Magnetic phase transitions

Charge-transfer insulators Mott insulators Strongly correlated systems Thin films

Density functional theory Epitaxy Mean field theory Resistivity measurements X-ray magnetic linear dichroism

Condensed Matter, Materials & Applied Physics

Authors & Affiliations

Jong-Woo Kim^1,*, Yongseong Choi ¹, S. Middey ², D. Meyers^3,†, J. Chakhalian⁴, Padraic Shafer ⁵, H. Park^6,7, and Philip J. Ryan^1,8

¹Advanced Photon Source, Argonne National Laboratory, Argonne, Illinois 60439, USA
²Department of Physics, Indian Institute of Science, Bangalore 560012, India
³Department of Condensed Matter Physics and Materials Science, Brookhaven National Laboratory, Upton, New York 11973, USA
⁴Department of Physics and Astronomy, Rutgers University, Piscataway, New Jersey 08854, USA
⁵Advanced Light Source, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA
⁶Department of Physics, University of Illinois at Chicago, Chicago, Illinois 60607, USA
⁷Materials Science Division, Argonne National Laboratory, Argonne, Illinois 60439, USA
⁸School of Physical Sciences, Dublin City University, Dublin 11, Ireland

^*jwkim@anl.gov
^†Present address: Physics Department, Oklahoma State University, Stillwater, Oklahoma 74078, USA.

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Issue

Vol. 124, Iss. 12 — 27 March 2020

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Images

Figure 1
(a) Temperature dependent resistivity (blue, left) and temperature dependence of $(\frac{1}{4} \frac{1}{4} \frac{1}{4})$ resonant soft x-ray magnetic reflection at the Ni $L_{3}$ edge (red, right). Inset: Reciprocal scan along surface normal ( $L$ direction). (b) The magnetic structure of the superlattice film showing 90° spin rotation with 4-unit-cell periodicity.
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Figure 2
(a) $L$ scan through $(\frac{1}{2} \frac{1}{2} \frac{1}{2})$ reflection. (b) $L$ scan through $(- \frac{1}{2} \frac{1}{2} \frac{1}{2})$ reflection. (c) Energy scans at the $(- \frac{1}{2} \frac{1}{2} \frac{1}{2})_{film}$ reflection at various temperatures. The nonresonant intensity rises with the temperature increases while the resonant intensity decreases. (d) Energy scans at the superstructure satellite peak $(- \frac{1}{2} \frac{1}{2} + \frac{1}{4})_{film}$ above and below the MIT. Because of the tail of the main resonant $(\frac{1}{2} \frac{1}{2} \frac{1}{2})$ reflection, the resonant component of Ni $K$ edge slightly increases below the transition. (e) Temperature dependence of scattering intensities on and off resonance illustrating the contrast between charge ordering and charge disproportionation, respectively. (f) Temperature dependence of the resonant scattering factor obtained by $I_{res}^{1 / 2} - I_{nonres}^{1 / 2}$ . Arrows in (c) indicated as $I_{res}$ and $I_{nonres}$ are the scattering intensities on and off resonant energies, respectively.
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Figure 3
(a) Octahedral rotation pattern of $a^{-} b^{-} c^{-}$ . All $a$ , $b$ , and $c$ are antiferrodistortive rotation axes (b) $a^{+} b^{-} c^{-}$ rotation pattern. The ferrodistortive axis is defined as the $c$ axis of the orthorhombic unit cell. (c) Breathing mode and charge disproportionation. (d) Superlattice structure of breathing mode without CD and (e) with CD. The breathing distortion decreases with the CD.
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Figure 4
(a) Illustration of x-ray resonant orbital scattering by switching between vertical ( $E / / c$ ) and horizontal ( $E / / a b$ ) polarizations with respect to Ni $3 d$ and $4 p$ orbital shapes. (b) X-ray linear dichroism (XLD) effects in x-ray absorption spectroscopy (XAS) across the Ni $K$ edge. (c) Anisotropy in orbitals reflected in polarization dependent reflectivity, sensitive to the bilayer anisotropy contrast. Blue and red curves are taken at on- and off-resonant energies indicated by arrows in (b). Polarization dependence is plotted as difference divided by sum, with the difference and sum between two curves with polarization parallel and perpendicular to the surface normal direction. Inset: Temperature dependence for the sum of the polarization anisotropy within the energy range indicated by the green rectangular box. The orbital anisotropy decreases below the transition temperature.
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