Source capture
Authors Abigail Y. Jiang, Maria Bambrick-Santoyo, Lopa Bhatt, Kyeong-Yoon Baek, Yi-Feng Zhao, Dan Ferenc Segedin, Ari B. Turkiewicz, Jenna Hatmin, Grace A. Pan, Suchismita Sarker, Donald A. Walko, Charles M. Brooks, David A. Muller, Berit H. Goodge, Hua Zhou, Antia S. Botana, Julia A. Mundy
arXiv / Publisher https://arxiv.org/abs/2606.20941
PDF https://arxiv.org/pdf/2606.20941
Relevance score 5.730
Primary category cond-mat.mtrl-sci
Published 2026-06-23
Research paradigm Both
Sample form Thin Film

Summary

This study systematically investigates the strain effect in trilayer nickelate La4Ni3O10 thin films through atomically precise synthesis, electrical transport measurements, picometer-resolution electron microscopy, and synchrotron X-ray diffraction. While compressive epitaxial strain effectively suppresses the parent density-wave order and enhances crystal symmetry (e.g., eliminating out-of-plane octahedral rotations), no superconductivity is observed even under the maximum compressive strain of -2.8%. Critical structural characterization reveals that compressive strain fails to completely eliminate the characteristic in-plane octahedral rotations in the thin films, which exhibit interlayer inequivalence between the inner and outer layers of each trilayer unit and persist robustly. Synchrotron X-ray diffraction shows that the amplitude of in-plane rotations decreases monotonically with compressive strain but does not vanish entirely. In contrast, in the bilayer system La3Ni2O7, compressive strain fully suppresses all octahedral rotations, thereby inducing superconductivity. These results uncover a key difference between trilayer and bilayer systems, indicating that ambient-pressure superconductivity in trilayer nickelates cannot be achieved solely through epitaxial strain engineering, and alternative tuning methods need to be explored.

Materials

Methods

Keywords

  • octahedral rotations
  • density wave suppression
  • layer inequivalence
  • compressive strain
  • absence of superconductivity
  • structural distortion

Highlights

  • We identify a previously unobserved structure in RP nickelates, the I4/mmm space group, demonstrating the capability of epitaxial strain to induce unique structural variants.
  • Compressive strain suppresses out-of-plane rotations but leaves in-plane rotations persistent, a structural evolution pathway distinct from that under hydrostatic pressure.

Conclusions

  • Compressive epitaxial strain suppresses the parent density wave in La4Ni3O10 thin films but does not induce superconductivity.
  • A structural distortion unique to strained n=3 thin films is identified: persistent, layer-inequivalent octahedral rotations around the c-axis.
  • These results highlight key differences between the n=3 and n=2 systems, suggesting that ambient-pressure superconductivity in the n=3 may require new methods beyond epitaxial strain engineering.

Main claims

  • Compressive epitaxial strain suppresses the parent density wave in La4Ni3O10 thin films but does not stabilize superconductivity.
    • Evidence: Transport measurements show no superconducting transition even at -2.8% compressive strain,Density wave transition is absent for compressive strains on LAO and SLAO
  • Compressive strain completely suppresses out-of-plane octahedral rotations in La4Ni3O10 thin films, raising crystal symmetry.
    • Evidence: ADF-STEM Fourier transforms show disappearance of half-order peaks under compressive strain
  • In-plane octahedral rotations persist in the inner perovskite layers even under large compressive strain, unlike in bilayer La3Ni2O7.
    • Evidence: Multislice electron ptychography shows persistent oxygen incoherence in inner layers for all strain states,Synchrotron XRD shows finite (1.5 0.5) peak even on SLAO
  • The structural evolution under compressive strain differs from that under hydrostatic pressure; in thin films, out-of-plane rotations are eliminated first, while in bulk, in-plane rotations are eliminated first.
    • Evidence: Thin film structural phases under compressive strain: a0 a0 c- with in-plane rotations,Bulk pressure phase diagram: a- a- c0 then a0 a0 c0

Workflow

  • Thin film synthesis — High qualityLa4Ni3O10 thin films with four distinct epitaxial strain states were successfully synthesized.
    • Materials: La; Ni; distilled ozone; pseudo-cubic substrates: SrLaAlO4 (SLAO), LaAlO3 (LAO), NdGaO3 (NGO), SrTiO3 (STO)
    • Methods: reactive oxygen molecular beam epitaxy (MBE) with dynamic layer-by-layer shuttering
    • Observations: High quality thin films with coherent strain; clear superlattice XRD peaks; Kiessig fringes; limited intergrowths
  • Electrical transport measurements — Compressive epitaxial strain suppresses the parent density wave order in La4Ni3O10 thin films, but does not induce superconductivity.
    • Materials: La4Ni3O10 thin films; Pt or Pd contacts
    • Methods: Resistivity vs temperature measurements; Hall effect measurements in PPMS with AC current; e-beam deposition of contacts; wirebonding
    • Observations: For tensile strain (NGO, STO): density wave transition observed at ≈134 K and ≈152 K respectively; For compressive strain (LAO, SLAO): no density wave transition observed; No superconducting transition for any film
  • Out-of-plane octahedral rotation analysis via ADF-STEM — Out-of-plane octahedral rotations are completely suppressed under compressive epitaxial strain, raising crystal symmetry from orthorhombic to tetragonal.
    • Materials: cross-sectional lamellas of La4Ni3O10 thin films
    • Methods: Annular dark-field scanning transmission electron microscopy (ADF-STEM); Fourier transform analysis of images
    • Observations: Tensile strain films (STO, NGO): clear half-order peaks indicating out-of-plane rotations; Compressive strain films (LAO, SLAO): no half-order peaks, indicating suppression of out-of-plane rotations
  • In-plane octahedral rotation analysis via multislice electron ptychography — In-plane octahedral rotations persist in the inner perovskite layers under all compressive strain states, even on SLAO with -2.8% strain.
    • Materials: cross-sectional lamellas of La4Ni3O10 thin films
    • Methods: Multislice electron ptychography (4D-STEM); maximum likelihood iterative phase retrieval; EMPAD-G2 detector
    • Observations: Inner perovskite layers show blurred oxygen columns due to in-plane rotations; Outer layers appear sharp; This blurring observed for all strain states including SLAO
  • Synchrotron X-ray diffraction for in-plane rotation quantification — In-plane octahedral rotation magnitude decreases monotonically with compressive strain but does not vanish completely.
    • Materials: La4Ni3O10 thin films on substrates
    • Methods: Crystal truncation rod (CTR) measurements at (1.5 0.5 L); high dynamic-range reciprocal space mapping (HDRM)
    • Observations: CTR peak intensity at (1.5 0.5 L) decreases with compressive strain; Barely detectable on SLAO; HDRM confirms systematic suppression of in-plane rotation signal
  • First-principles calculations — First-principles calculations corroborate experimental findings on structural evolution and density wave suppression.
    • Materials: La4Ni3O10 crystal structure models
    • Methods: Density functional theory (DFT) using GGA+U; QUANTUM ESPRESSO implementation
    • Observations: Calculations reproduce suppression of out-of-plane rotations under compressive strain; Persistence of in-plane rotations confirmed; Density wave instability suppression predicted