Source capture
Authors Ziao Han, Lifen Xiang, Tianren Wang, Congcong Le, Jun Zhan, Siyi Lei, Sonia Francoual, Qisi Wang, Jiangping Hu, Tao Xiang, Ronny Sutarto, Xianxin Wu, X. J. Zhou, Zhihai Zhu
arXiv / Publisher https://arxiv.org/abs/2610.01757
PDF https://arxiv.org/pdf/2610.01757
Relevance score 5.632
Primary category cond-mat.supr-con
Published 2026-10-02
Research paradigm Both
Sample form Thin Film

Summary

This study investigates the interplay of spin density wave (SDW) and charge-anisotropy-like order with superconductivity in bilayer nickelate films by combining ozone annealing and isovalent rare-earth A-site substitution to effectively apply c-axis uniaxial pressure and tune interlayer coupling. Resonant elastic X-ray scattering shows that, upon optimizing superconductivity, the SDW transition temperature decreases from 150 K to 70 K; although weakened, the SDW persists, whereas the charge-anisotropy-like order is completely eliminated in the superconducting state. Polarization-resolved O K-edge X-ray absorption spectroscopy and electronic structure calculations indicate that both the c-axis compression induced by A-site substitution and the filling of interlayer oxygen vacancies by ozone annealing enhance interlayer Ni-O-Ni hybridization, reconstruct the Fermi surface, and suppress magnetic fluctuations near the SDW wave vector, thereby weakening the SDW instability. These results indicate that the two electronic orders are governed by different energy scales and are consistent with a spin–spinless stripe ground state, providing new clues for understanding density-wave formation and its relationship to superconductivity in bilayer nickelates.

Materials

Methods

  • PLD
  • ozone-assisted annealing
  • resonant elastic X-ray scattering (REXS)
  • polarization-resolved O K-edge X-ray absorption spectroscopy (XAS)
  • X-ray linear dichroism (XLD)
  • hard X-ray diffraction
  • DFT
  • VASP
  • Wannier90
  • magnetic susceptibility calculations

Keywords

Highlights

  • Selectively suppresses two distinct electronic orders in bilayer nickelate thin films by tuning interlayer coupling through rare-earth A-site substitution and ozone annealing.
  • Realizes superconducting bilayer nickelate films with TSDW tuned from 150 K down to 70 K.
  • Shows that the charge-like anisotropy order is completely eliminated in the superconducting state while the SDW order persists but weakens.
  • Identifies two distinct routes—c-axis compression from A-site substitution and filling of interlayer oxygen vacancies by ozone annealing—that both enhance interlayer Ni-O-Ni hybridization.
  • Provides new constraints on the origin of density waves and their relationship to superconductivity in bilayer nickelates.

Conclusions

  • Combining oxygen annealing with isovalent rare-earth A-site substitution effectively applies c-axis uniaxial pressure and realizes superconducting bilayer nickelate films with the SDW transition temperature suppressed from 150 K to 70 K.
  • While SDW order is weakened but remains, a second charge-like anisotropy order is completely eliminated in the superconducting state, showing that the two electronic orders are governed by different energy scales.
  • Polarization-resolved O K-edge X-ray absorption and electronic structure calculations show that strengthened interlayer coupling reconstructs the Fermi surface, reduces inter-pocket scattering, and weakens spin fluctuations near the SDW wavevector.
  • The findings are consistent with a spin–spinless stripe ground state; the suppression of SDW order can be explained by an itinerant Fermi-surface-driven scenario, whereas the disappearance of the charge-like anisotropy order points to the essential role of electronic correlations.

Main claims

  • Combining oxygen annealing with isovalent rare-earth A-site substitution effectively applies c-axis uniaxial pressure and tunes interlayer coupling, realizing superconducting bilayer nickelate films with TSDW suppressed from 150 K to 70 K.
    • Evidence: Abstract: 'combine oxygen annealing with isovalent rare-earth (A-site) substitution to effectively apply c-axis uniaxial pressure, realizing superconducting bilayer nickelate films with TSDW suppressed from 150 K to 70 K.',Summary: combining ozone annealing and isovalent rare-earth A-site substitution tunes interlayer coupling and decreases SDW transition temperature from 150 K to 70 K upon optimizing superconductivity.
  • The SDW order is weakened but remains, while a second charge-like anisotropy order is completely eliminated in the superconducting state.
    • Evidence: Abstract: 'while SDW order is weakened but remains, a second charge-like anisotropy order is completely eliminated in the superconducting state.',Full text: 'the SDW is progressively weakened but persists, whereas the channel charge-like order is completely eliminated upon substitution with Pr or Sm.',Full text: 'the charge-like anisotropy order is even more sensitive: its characteristic non-monotonic temperature profile … is completely suppressed once superconductivity is established.'
  • Polarization-resolved O K-edge X-ray absorption and electronic structure calculations show that strengthened interlayer coupling reconstructs the Fermi surface and weakens the SDW.
    • Evidence: Abstract: 'Polarization-resolved O K-edge X-ray absorption and electronic structure calculations show that strengthened interlayer coupling reconstructs the Fermi surface and weakens the SDW.',Full text: 'This strain enhances the interlayer coupling, expanding the pocket while contracting the pocket. As a result, the inter-pocket scattering is reduced, which leads to a decrease in the odd-channel magnetic susceptibility near the SDW wavevector.'
  • The two electronic orders are governed by different energy scales and respond differently to the same tuning.
    • Evidence: Full text: 'This selective suppression demonstrates that the two orders are not governed by a single energy scale.',Full text: 'the SDW weakens progressively as superconductivity is optimized, whereas the charge-like anisotropy order is completely eliminated.'
  • The results are consistent with a spin-spinless stripe ground state and suggest different roles for itinerant Fermi-surface nesting and electronic correlations.
    • Evidence: Abstract: 'These findings, consistent with a spin-spinless stripe ground state, provide new insight into the mechanism of density wave formation and their interplay with superconductivity.',Full text conclusion: 'the suppression of the channel SDW order can be consistently explained by an itinerant, Fermi surface-driven scenario … the complete disappearance of the channel charge-like anisotropy order … points to the essential role of electronic correlations.'

Workflow

  • sample_preparation — Combining rare-earth A-site substitution and ozone annealing tunes interlayer coupling in bilayer nickelate thin films.
    • Materials: La2PrNi2O7-δ (LPNO) thin films; La3Ni2O7-δ (LNO) thin films; La2SmNi2O7-δ (LSNO) thin films; (001)-oriented LaAlO3 (LAO) substrates; (001)-oriented SrLaAlO4 (SLAO) substrates; stoichiometric polycrystalline target; ozone
    • Methods: pulsed laser deposition using a 248-nm KrF excimer laser; ozone-assisted annealing following an oxygen recycling protocol; X-ray reflectivity thickness calibration
    • Observations: Ozone annealing produced superconducting LPNO/SLAO films, whereas thicker LPNO/LAO films remained non-superconducting.; Ozone annealing fills interlayer oxygen vacancies and restores the Ni-O-Ni interlayer hybridization channel.
  • measurement — REXS and polarization-resolved XAS track the selective suppression of SDW and charge-like anisotropy orders and changes in interlayer hybridization.
    • Materials: LPNO/LAO films; LPNO/SLAO films; LNO/SLAO films; LSNO/SLAO films
    • Methods: resonant elastic X-ray scattering (REXS) at the Ni L-edge and O K-edge; polarization-resolved X-ray absorption spectroscopy (XAS) in total electron yield and total fluorescence yield modes; hard X-ray diffraction; temperature-dependent REXS momentum scans with Lorentzian peak fitting
    • Observations: REXS detects SDW order and a second charge-like anisotropy order with different polarization responses.; Ozone annealing suppresses the resonant peak intensity and shifts the SDW transition temperature.; The non-monotonic temperature profile of the charge-like anisotropy order disappears after ozone annealing.; O K-edge XAS out-of-plane spectra show restoration of low-energy spectral weight after ozone annealing, indicating increased interlayer hybridization.
  • analysis — Enhanced interlayer coupling reconstructs the Fermi surface and suppresses spin fluctuations near the SDW wavevector.
    • Materials: REXS data; XAS data; electronic structure models
    • Methods: band structure calculations using the projector augmented wave method in VASP; Perdew-Burke-Ernzerhof exchange-correlation functional; Wannier90 maximally localized Wannier functions for Ni orbitals; magnetic susceptibility evaluation; O K-edge XAS simulations using an excited-electron and core-hole approach; comparison of experimental spectra with calculated electronic structure
    • Observations: A-site substitution modeled as c-axis compression enhances interlayer coupling, expands the pocket, and contracts the pocket.; Enhanced interlayer coupling reduces inter-pocket scattering and decreases odd-channel magnetic susceptibility near the SDW wavevector.; Calculated O K-edge XAS links low-energy out-of-plane spectral weight primarily to interlayer apical oxygens.
  • interpretation — SDW suppression is consistent with an itinerant Fermi-surface-driven scenario, whereas elimination of the charge-like anisotropy order points to electronic correlations and the spin-spinless stripe framework.
    • Methods: unified framework combining REXS, XAS, hard X-ray diffraction, and first-principles calculations; comparison with the spin-spinless stripe framework
    • Observations: SDW order weakens but persists, while charge-like anisotropy order is completely eliminated in the superconducting state.; The temperature dependence of SDW integrated intensity shows no anomaly at Tc, indicating no direct competition between SDW order and superconductivity.; Selective suppression indicates that the two electronic orders are not governed by a single energy scale.