来源 自动抓取
作者 Hengyang Zhong, Bo Hao, Zhijia Zhang, Anni Chen, Yuan Wei, Ruixian Liu, Xinru Huang, Chunyi Li, Wenting Zhang, Chang Liu, Xiao-Sheng Ni, Marli dos Reis Cantarino, Kurt Kummer, Nicholas Brookes, Kun Cao, Yuefeng Nie, Thorsten Schmitt, Xingye Lu
arXiv / 出版方 https://arxiv.org/abs/2502.03178
PDF https://arxiv.org/pdf/2502.03178
相关度评分 5.670
主分类 cond-mat.supr-con
发布日期 2026-06-10
研究范式 实验研究
样品形态 薄膜

摘要

该工作利用共振非弹性X射线散射（RIXS）系统研究了外延应变从约-2%至+1.9%的La3Ni2O7（LNO）薄膜的电子和自旋激发。在呈现常压超导（起始转变温度>40 K）的压缩应变LNO/SrLaAlO4薄膜中，观察到与块材LNO相似的dd激发和自旋动力学，但自旋激发带宽增大约10 meV，表明层间反铁磁交换作用Jz增强；而拉伸应变的LNO/SrTiO3薄膜则表现出自旋激发和Ni 3dz2相关dd激发的显著抑制。这一演化反映了应变对Ni 3dz2-O 2pz杂化和层间距离的调控，进而影响层间磁耦合强度。结果表明，外延应变能有效调制双层镍酸盐的层间反铁磁超交换作用，且增强的Jz与常压超导的出现密切相关，支持层间磁交换作用促进层间配对的理论图像。

材料

方法

关键词

亮点

  • The LNO/SLAO thin film exhibits dispersive spin excitations similar to bulk La3Ni2O7 but with a larger spin-excitation bandwidth, indicating enhanced interlayer antiferromagnetic exchange Jz under compressive strain.
  • Tensile-strained LNO/STO shows a marked suppression of both spin excitations and Ni 3dz2-derived dd excitations, reflecting a collapse of magnetic correlations.
  • The emergence of ambient-pressure superconductivity with onset >40 K in compressively strained La3Ni2O7 films coincides with the strengthening of interlayer antiferromagnetic superexchange.
  • The results demonstrate how epitaxial strain modulates interlayer magnetic coupling and provide direct spectroscopic evidence linking structural reconstruction, spin dynamics, and superconductivity.

结论

  • High-resolution Ni- RIXS reveals robust, dispersive spin excitations in the LNO/SLAO thin film and establishes the systematic evolution of magnetic correlations under epitaxial strain.
  • The interlayer exchange is not dictated by a single geometric parameter, but is instead governed by the synergistic structural modulation of the Ni-OAP-Ni bond angle and the c-axis lattice constant, which collectively tune the effective Ni 3dz2–O 2pz hybridization.
  • The enhancement of interlayer antiferromagnetic superexchange under compressive strain, and the contrasting profound collapse of overall magnetic spectral weight under tensile strain, closely track the emergence and disappearance of the superconducting phase.
  • These direct spectroscopic constraints are highly consistent with pairing scenarios wherein interlayer magnetic exchange interactions, acting within a delicately balanced structural framework, serve as a key ingredient for superconductivity in bilayer nickelates.

主要论断

  • Compressively strained LNO/SLAO thin films exhibit dispersive spin excitations similar to bulk LNO but with a larger bandwidth, indicating enhanced interlayer antiferromagnetic exchange Jz.
    • 证据: RIXS spectra along (H,0) and (0,0,L) show dispersive magnon with band top energy ≈10 meV higher than bulk,Heisenberg model fitting gives Jz = 58 meV for LNO/SLAO vs 50 meV for bulk
  • Tensile strain in LNO/STO suppresses both spin excitations and Ni 3dz2-derived dd excitations, reflecting weakened interlayer magnetic coupling and hybridization.
    • 证据: RIXS spectra of LNO/STO show no distinct magnetic peak, DHO fit gives upper bound Jz ≤ 35 meV,dd excitation at 1.6 eV suppressed in tensile-strained films
  • Epitaxial strain modulates interlayer magnetic coupling via synergistic effects on Ni-OAP-Ni bond angle and c-axis lattice constant, which collectively tune Ni 3dz2-O 2pz hybridization.
    • 证据: Structural characterization: bond angle from 164° to 172° across strain range,dd excitation intensity tracks hybridization changes,Jz values correlate with strain and bond angle
  • The correlation between enhanced Jz and superconductivity supports theoretical scenarios where interlayer antiferromagnetic superexchange promotes interlayer pairing in bilayer nickelates.
    • 证据: Superconductivity (Tc,onset > 40 K) observed only in compressively strained LNO/SLAO,LNO/STO with suppressed Jz shows no superconductivity,Theoretical models: interlayer pairing mediated byJz

研究流程

  • sample_preparation — Epitaxially strained La3Ni2O7 thin films were grown on various substrates to systematically vary in-plane strain.
    • 材料: La3Ni2O7 thin films; SrLaAlO4 (SLAO) substrate; LaAlO3 (LAO) substrate; (LaAlO3)0.3(Sr2TaAlO6)0.7 (LSAT) substrate; SrTiO3 (STO) substrate
    • 方法: reactive molecular-beam epitaxy (MBE); post-growth ozone annealing (for LNO/SLAO)
    • 观察: high-quality films confirmed by XRD and RSM
  • measurement — High-resolution RIXS revealed strain-dependent electronic and spin excitations in LNO thin films.
    • 材料: resonant inelastic X-ray scattering (RIXS) at ID32, ESRF; Ni L3-edge X-rays
    • 方法: X-ray absorption spectroscopy (XAS) total fluorescence yield; RIXS with pi-polarized incident photons; momentum-dependent scans along (H,0) and (0,0,L); grazing incidence geometry
    • 观察: dispersive spin excitations in LNO/SLAO and LNO/LAO; suppressed spin excitations and broadened dd excitations in LNO/STO
  • analysis — Quantitative analysis shows compressive strain enhances interlayer exchange Jz, while tensile strain severely suppresses it.
    • 材料: SpinW code
    • 方法: damped harmonic oscillator (DHO) fitting of RIXS spectra; classical Heisenberg model fitting of magnon dispersion; comparison of magnon energies and spectral weights
    • 观察: LNO/SLAO magnon bandwidth ≈10 meV larger than bulk; LNO/STO magnon energies reduced by >30 meV, spectral weight suppressed >80%
  • interpretation — Strain-tuned interlayer antiferromagnetic superexchange Jz is a key factor for superconductivity, consistent with spin-fluctuation-mediated pairing theories.
    • 方法: correlation with superconductivity observations; comparison with theoretical pairing scenarios
    • 观察: superconductivity only in compressively strained films; enhanced Jz in LNO/SLAO, collapsed magnetic correlations in LNO/STO