Electronic structure and magnetic correlations in the epitaxially strained bilayer nickelate La₃Ni₂O₇

摘要

本文采用DFT+动力学平均场理论方法，研究了电子关联和外延应变对双层Ruddlesden-Popper镍酸盐La₃Ni₂O₇正常态电子结构、准粒子重整化、费米面及磁关联的影响。结果表明Ni 3d能带存在显著的轨道选择性重整化和强非相干性，Ni的x²−y²与3z²−r²态接近轨道选择性局域化。电子性质对面内应变高度敏感：拉伸应变和约−2%以内的中等压缩应变均能显著增强磁关联；而在约−4%的大压缩应变下，体系发生Lifshitz转变，γ费米面片消失，该费米面片与几乎完全占据的、浅的成键Ni 3z²−r²平带相关，并导致磁关联急剧下降，暗示超导被抑制。总体上，结果支持自旋/电荷密度波条纹不稳定性由费米面嵌套驱动的图像，并表明压力和应变可有效调控自旋-电荷密度波有序，从而增强自旋涨落。

材料

• La₃Ni₂O₇

方法

• DFT+DMFT
• Quantum ESPRESSO
• Wannier functions
• CT-QMC
• Padé approximants
• particle-hole bubble approximation

关键词

• orbital selective renormalization
• magnetic correlations
• epitaxial strain
• lifshitz transition
• fermi surface nesting
• spin charge density wave stripe instability
• orbital selective localization
• spin fluctuations
• superconductivity suppression

亮点

• The Ni 3d bands exhibit pronounced orbital-selective renormalization and strong incoherence, pointing to the proximity of the Ni x2-y2 and 3z2-r2 states to orbital-selective localization.
• The electronic properties of La₃Ni₂O₇ are highly sensitive to in-plane strain, with tensile and moderate compressive strain up to about -2% enhancing magnetic correlations compared to the unstrained system.
• Under large compressive strain of about -4%, a Lifshitz transition occurs with the disappearance of the gamma Fermi surface sheet, associated with a nearly fully occupied, shallow flat band of bonding Ni 3z2-r2 orbital character.
• The work supports spin- and charge-density-wave stripe instability driven by Fermi surface nesting and suggests that pressure and strain can suppress or enhance spin-charge-density-wave ordering, enhancing spin fluctuations.

结论

• Using DFT+DMFT, the normal-state electronic properties of epitaxially strained La₃Ni₂O₇ show a remarkable orbital-selective renormalization of the Ni 3d bands, with the Ni x2-y2 and 3z2-r2 states approaching orbital-selective localization.
• Both tensile strain and moderate compressive strain up to about -2% significantly enhance magnetic correlations relative to unstrained La₃Ni₂O₇, while a large compressive strain of about -4% induces a Lifshitz transition marked by the disappearance of the gamma Fermi surface sheet.
• The disappearance of the gamma Fermi surface sheet, associated with a nearly fully occupied shallow flat band of bonding Ni 3z2-r2 character, causes a sharp decrease of magnetic correlations and implies suppression of superconductivity.
• The results support the picture that spin- and charge-density-wave stripe instability is driven by Fermi surface nesting in La₃Ni₂O₇, and that pressure and strain can tune spin-charge-density-wave ordering, giving rise to enhanced spin fluctuations.

主要论断

• Ni 3d bands in La₃Ni₂O₇ exhibit pronounced orbital-selective renormalization and strong incoherence, with the Ni x2-y2 and 3z2-r2 states approaching orbital-selective localization.
  • 证据: Full text: Our results exhibit a remarkable orbital-selective renormalization and strong incoherence of the Ni bands, pointing to the proximity of the Ni and states to orbital-selective localization.,Abstract: Our results exhibit a remarkable orbital-selective renormalization and strong incoherence of the Ni 3d bands, pointing to the proximity of the Ni x2-y2 and 3z2-r2 states to orbital-selective localization.
• Tensile strain and moderate compressive strain up to about -2% significantly enhance magnetic correlations compared with unstrained La₃Ni₂O₇.
  • 证据: Full text: We note that both a tensile and a moderate compressive strain (up to about %) yield a significant enhancement of magnetic correlations compared to the unstrained LNO.,Abstract: We note that both a tensile and a moderate compressive strain (up to about -2%) yield a significant enhancement of magnetic correlations compared to the unstrained LNO.
• Under a large compressive strain of about -4%, La₃Ni₂O₇ undergoes a Lifshitz transition characterized by the disappearance of the γ Fermi surface sheet associated with a nearly fully occupied shallow bonding Ni 3z2-r2 flat band.
  • 证据: Full text: Under a large compressive strain of about %, we observe a Lifshitz transition characterized by the disappearance of the Fermi surface sheet, which is associated with a nearly fully occupied, shallow flat-band of the bonding Ni orbital character.,Abstract: Under a large compressive strain of about -4%, we observe a Lifshitz transition characterized by the disappearance of the γ Fermi surface sheet, which is associated with a nearly fully occupied, shallow flat-band of the bonding Ni 3z2-r2 orbital character.
• The Lifshitz transition leads to a sharp decrease in magnetic correlations, implying suppression of superconductivity.
  • 证据: Full text: As a result, we observe a sharp decrease of magnetic correlations, implying suppression of superconductivity.,Abstract: As a result, we observe a sharp decrease of magnetic correlations, implying suppression of superconductivity.
• The results support a spin- and charge-density-wave stripe instability driven by Fermi surface nesting, and pressure and strain can tune this ordering while enhancing spin fluctuations.
  • 证据: Full text: Overall, our results support the picture of spin- and change-density-wave stripe instability driven by the Fermi surface nesting in LNO.,Abstract: Our results suggest that both pressure and strain can effectively tune (suppress or enhance) spin-change-density-wave ordering, giving rise to enhanced spin fluctuations.

研究流程

• model_setup_and_structure_relaxation — Structural models were generated for unstrained and biaxially strained La₃Ni₂O₇.
  • 材料: La₃Ni₂O₇ bilayer Ruddlesden-Popper nickelate
  • 方法: nonmagnetic density functional theory structural optimization; Perdew-Burke-Ernzerhof exchange functional; Quantum ESPRESSO
  • 观察: -2% compressive strain gives in-plane lattice constant ≈3.747 Å and ≈1.7% c-axis elongation; +2% tensile strain gives ≈1.4% c-axis reduction
• electronic_structure_calculation — DFT+DMFT calculations show strongly correlated Ni 3d states with orbital-selective behavior.
  • 材料: Ni 3d, La 5d, and O 2p Wannier basis
  • 方法: fully charge self-consistent DFT+dynamical mean-field theory; continuous-time hybridization expansion quantum Monte Carlo; Hubbard U and Hund's exchange J with fully localized double-counting correction; Padé analytic continuation
  • 观察: orbital-selective quasiparticle mass renormalization and strong incoherence of Ni 3d states; bonding-antibonding splitting of Ni 3z2-r2 states of about 1.16 eV
• analysis — Strain-dependent electronic structure, Fermi surface topology, and magnetic correlations were systematically mapped.
  • 方法: k-resolved spectral functions; orbital-dependent quasiparticle band renormalization analysis; Fermi surface mapping; local spin susceptibility and momentum-resolved static magnetic susceptibility within particle-hole bubble approximation
  • 观察: Fermi surface contains α and β sheets plus a γ sheet near the Brillouin zone M point; γ sheet disappears under about -4% compressive strain, indicating a Lifshitz transition; magnetic correlations are enhanced for tensile and moderate compressive strain up to about -2%, then drop sharply at about -4%
• interpretation — The results support a spin- and charge-density-wave stripe instability driven by Fermi surface nesting, with pressure and strain tuning the ordering and spin fluctuations.
  • 方法: comparison of Fermi surface nesting features and calculated magnetic susceptibility with spin/charge density wave stripe scenario
  • 观察: major magnetic instability near the M point and Γ-X branch; magnetic correlations are associated with incommensurate wave vectors near the M point and Γ-X branch