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Ultrafast transient increase of oxygen octahedral rotations in a perovskite

M. Porer, M. Fechner, M. Kubli, M. J. Neugebauer, S. Parchenko, V. Esposito, A. Narayan, N. A. Spaldin, R. Huber, M. Radovic, E. M. Bothschafter, J. M. Glownia, T. Sato, S. Song, S. L. Johnson, and U. Staub
Phys. Rev. Research 1, 012005(R) – Published 9 August 2019
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    Abstract

    We present femtosecond hard x-ray diffraction experiments that study the effect of photodoping on the perovskite EuTiO3. We observe an ultrafast transient increase of reflection intensities that are directly related to the antiferrodistortive rotation of the oxygen octahedra. This increase relates directly to an increase of the order parameter associated with a purely structural phase transition that is opposite to the behavior of increasing the materials temperature. First-principles calculations show that the creation of electron-hole pairs leads to changes in the vibrational potential that is consistent with an increase of the order parameter. The order parameter increase can be understood from an ultrafast charge-transfer-induced reduction of the Goldschmidt tolerance factor, which is a fundamental control parameter for the properties of perovskites.

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    • Received 14 February 2019

    DOI:https://doi.org/10.1103/PhysRevResearch.1.012005

    Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI.

    Published by the American Physical Society

    Physics Subject Headings (PhySH)

    1. Research Areas
    Dynamical phase transitionsLattice dynamicsOrder parameters
    1. Techniques
    Density functional theoryX-ray diffraction
    Condensed Matter, Materials & Applied Physics

    Authors & Affiliations

    M. Porer1,*, M. Fechner2, M. Kubli3, M. J. Neugebauer3, S. Parchenko1, V. Esposito4, A. Narayan5, N. A. Spaldin5, R. Huber6, M. Radovic1, E. M. Bothschafter1, J. M. Glownia7, T. Sato7, S. Song7, S. L. Johnson3,4, and U. Staub1,†

    • 1Swiss Light Source, Paul Scherrer Institute, 5232 Villigen-PSI, Switzerland
    • 2Max Planck Institute for the Structure and Dynamics of Matter, CFEL, 22761 Hamburg, Germany
    • 3Institute for Quantum Electronics, ETH Zürich, 8093 Zürich, Switzerland
    • 4SwissFEL, Paul Scherrer Institute, 5232 Villigen-PSI, Switzerland
    • 5Materials Theory, ETH Zürich, 8093 Zürich, Switzerland
    • 6Department of Physics, University of Regensburg, 93040 Regensburg, Germany
    • 7LCLS, SLAC National Accelerator Laboratory, Menlo Park, California 94025, USA

    • *science@porer.org
    • †Urs.Staub@psi.ch

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    Vol. 1, Iss. 1 — August 2019

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    • Figure 1
      Figure 1

      (a) Ti (blue) and O (red) atoms of two cubic unit cells stacked along the c axis. Arrows indicate atomic motions of the oxygen sites during the AFD transition and the direction of the octahedral rotation angle φ. (b) Equilibrium rocking curve of a typical superlattice reflection of the 40-nm thin EuTiO3 film measured at T=120K. (c) Dynamics of the 523212 superlattice reflection intensity upon photoexcitation at T=120K. The labels denote the pump photon energy and the absorbed excitation fluence. The blue and red solid lines result from a fit of the phenomenological model explained in the text and the Supplemental Material [25]. The green solid line is a guide to the eye. Inset: Schematic of the femtosecond x-ray diffraction (XRD) experiment.

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    • Figure 2
      Figure 2

      Transient superlattice diffraction intensity for a series of excitation fluences. The pump photon energy is set to 3.1eV and the temperature is 120K. The solid lines are derived from a numerical fit to the model described in the text.

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    • Figure 3
      Figure 3

      (a) Calculated EuTiO3 total density of states (DOS) in equilibrium and for an e−h concentration of 0.05 e−h/f.u. (dotted line). Zero is set to the bottom of the conduction band. Arrows indicate the charge-transfer excitations for photon energies of 1.55 eV (red), 3.1 eV (blue), 4.65 eV (green.) Right inset: Slice in the (101) plane of the e−h induced total e− density difference (blue/red: increase/decrease of electron density). Left inset: Zoom of the DOS in the vicinity of the Fermi level. The solid areas show the density of doped holes (red) and electrons (blue). (b) Double-well potential of the AFD soft mode calculated for a series of e−h concentrations ρ.

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