Nearly perfect Fermi surface nesting in hole-doped La₃Ni₂O₇ enables bulk superconductivity without pressure or strain

摘要

通过结合密度泛函理论、动态平均场理论和随机相位近似求解超导能隙方程，研究者发现空穴掺杂的层状镍氧化物La_3-xSr_xNi₂O₇在环境压力下可实现体超导电性。当掺杂浓度x接近0.4时，Ni-d₃z²_-r²轨道衍生的γ费米口袋从圆形演变为菱形并扩展至半个布里渊区，形成近乎完美的费米面嵌套，最佳嵌套矢量为Q=(π, π)。这一结构显著增强了反铁磁自旋涨落，将超导特征值提升至实验可观测的水平，无需施加高压或应变。该工作阐明了空穴掺杂调控费米口袋形状与大小的机制，为在常压下实现此类材料长期追求的体超导提供了理论依据和实验可行路径。

材料

• La_3-xSr_xNi₂O₇

方法

• DFT
• DMFT
• Random phase approximation (RPA)
• Linearized gap equation

关键词

• fermi surface nesting
• antiferromagnetic spin fluctuations
• superconducting eigenvalue
• hole doping
• γ pocket
• s± wave pairing
• ambient pressure superconductivity

亮点

• Provides a robust mechanism and an experimentally feasible route to inducing the long-sought bulk superconductivity in La₃Ni₂O₇ without pressure or strain.
• The diamond-shaped γ pocket at x=0.4 exhibits nearly perfect Fermi surface nesting, substantially increasing the leading superconducting eigenvalue to an experimentally observable level.
• First proposal to achieve ambient-pressure bulk superconductivity in RP nickelates via hole doping (Sr substitution).
• Identifies optimal doping x=0.4 where the γ pocket exhibits nearly perfect nesting, leading to a substantial increase in superconducting eigenvalue.

结论

• A substantially increased superconducting eigenvalue is found in bulk La_3-xSr_xNi₂O₇ at x=0.4 under ambient pressure, yielding observable superconductivity.
• The underlying mechanism is that hole doping induces a Ni-d3z2-r2-derived γ pocket that evolves from circular to diamond-shaped and expands to span half of the Brillouin zone, resulting in nearly perfect Fermi surface nesting with optimal nesting vector Q=(π,π), which enhances antiferromagnetic spin fluctuations and induces unconventional superconductivity.
• Hole doping induces a Ni-dz2-derived γ pocket on the Fermi surface; at x=0.4, the pocket becomes diamond-shaped and spans half of the Brillouin zone, achieving nearly perfect Fermi surface nesting with vector Q=(π,π).
• This nesting strongly enhances antiferromagnetic spin fluctuations and substantially increases the leading superconducting eigenvalue to an experimentally observable level.
• Provides a mechanism and feasible experimental route to achieving bulk superconductivity in La₃Ni₂O₇ without pressure or strain.

主要论断

• Hole doping induces a Ni-d3z2-r2 derived γ pocket that evolves from circular to diamond-shaped as x approaches 0.4, resulting in nearly perfect Fermi surface nesting.
  • 证据: Full text: 'As x approaches 0.4, the γ pocket evolves from circular to diamond-shaped and expands to span half of the Brillouin zone, resulting in nearly perfect Fermi surface nesting with the optimal nesting vector Q = (π, π).'
• This nesting enhances antiferromagnetic spin fluctuations and substantially increases the leading superconducting eigenvalue to yield experimentally observable superconductivity at ambient pressure.
  • 证据: Abstract: '…strongly enhances antiferromagnetic spin fluctuations and substantially increases the leading superconducting eigenvalue to a level at which superconductivity becomes experimentally observable.'
• Hole doping at x=0.4 induces nearly perfect Fermi surface nesting and enhances antiferromagnetic spin fluctuations, leading to observable superconductivity
  • 证据: From abstract: 'As x approaches 0.4, the γ pocket evolves from circular to diamond-shaped and expands to span half of the Brillouin zone, resulting in nearly perfect Fermi surface nesting with the optimal nesting vector Q = (π, π). This, in turn, strongly enhances antiferromagnetic spin fluctuations and substantially increases the leading superconducting eigenvalue'

研究流程

• Electronic structure calculation — Hole doping serves as a tuning parameter for size and shape of the γ pocket
  • 材料: La₃Ni₂O₇ crystal structure
  • 方法: Density functional theory (DFT); Dynamical mean-field theory (DMFT)
  • 观察: Hole doping induces a Ni-d3z2-r2 derived γ pocket on Fermi surface
• Superconducting gap equation solution — Leading superconducting eigenvalue increases to experimentally observable level
  • 材料: Bilayer two-orbital model fitted to DFT bands
  • 方法: Random phase approximation (RPA); Linearized gap equation
  • 观察: Nearly perfect Fermi surface nesting with nesting vector Q=(π,π); Enhanced antiferromagnetic spin fluctuations
• density_functional_theory_calculations — Obtained non-interacting electronic structure
  • 材料: La_3-xSr_xNi₂O₇ bulk
  • 方法: DFT with PBE functional
  • 观察: band structure; Fermi surface
• dynamical_mean_field_theory_calculations — Obtained interacting electronic structure
  • 材料: Bilayer two-orbital model
  • 方法: DMFT with Slater-Kanamori interaction
  • 观察: quasiparticle dispersion; quasiparticle weight
• random_phase_approximation_analysis — At x=0.4, nearly perfect Fermi surface nesting enhances spin fluctuations and superconducting eigenvalue
  • 材料: DMFT quasiparticle energies
  • 方法: RPA+DMFT for spin susceptibility and pairing potential
  • 观察: leading superconducting eigenvalue; spin susceptibility