Hall Coefficient Sign Reversal Driven by Orbital-Selective Oxygen-Vacancy Scattering in Nickelate Films

摘要

该研究结合DFT+CDMFT导出的关联多轨道准粒子模型与T矩阵方法，在半经典玻尔兹曼输运框架中处理氧空位散射，揭示了双层镍酸盐薄膜中霍尔系数符号反转的微观起源。多带补偿本身并不足以解释这一现象；面内氧空位通过轨道选择性散射强烈压制由dx^2-_y²轨道主导的输运通道，驱动霍尔系数穿越零值而变为正，而顶点氧空位却使霍尔系数更趋向负值。这一口袋分辨和轨道选择性的氧空位散射机制表明，氧空位不仅是电子掺杂源，更是活跃的散射中心，其空间分布直接调控正常态输运行为，为统一理解实验中随氧化学计量比变化的多样霍尔响应提供了理论框架。

材料

• La₃Ni₂O₇ bilayer nickelate

方法

• DFT+CDMFT
• T-matrix method
• semiclassical Boltzmann transport
• DFT-Wannier workflow
• first-principles calculations

关键词

• hall coefficient sign reversal
• orbital selective scattering
• oxygen vacancies
• multiband compensation
• transport relaxation time
• pocket resolved contributions
• rigid band doping

亮点

• A correlated multi-orbital quasiparticle model with T-matrix treatment of oxygen-vacancy scattering provides a unified microscopic explanation for the Hall coefficient sign reversal.
• In-plane and inner-apical oxygen vacancies have qualitatively different effects on the Hall coefficient due to orbital-selective scattering, rooted in the distortion of the local crystal-field environment.
• The study demonstrates that oxygen vacancies act as active scattering centers beyond simple electron doping, with their spatial distribution being a key control parameter for transport properties.
• The theoretical framework reconciles the seemingly contradictory Hall data across different nickelate films by accounting for oxygen stoichiometry and vacancy distribution.

结论

• Multiband compensation by itself cannot account for the Hall coefficient sign reversal in bilayer nickelate films.
• In-plane oxygen vacancies selectively suppress the dx2-y2 orbital transport channel, driving the Hall coefficient from negative to positive, while inner-apical vacancies make it more negative.
• Orbital-selective oxygen-vacancy scattering, rather than rigid-band electron doping, is the microscopic origin of the sign reversal.
• The results provide a framework for understanding the diverse Hall responses observed in nickelate films as a function of oxygen stoichiometry.

主要论断

• Orbital-selective oxygen-vacancy scattering drives the Hall coefficient sign reversal in bilayer nickelate films.
  • 证据: In-plane vacancies suppress the transport channel dominated by the dx2-y2 orbital, driving R_H positive.,Inner-apical vacancies make R_H more negative and do not produce a sign change.,Mixed distributions with sufficient in-plane vacancy fraction reverse sign.
• Multiband compensation alone cannot explain the Hall coefficient sign reversal; oxygen-vacancy scattering is necessary to select the competing channels.
  • 证据: Rigid-band doping calculations show R_H remains negative over the considered range.,Without vacancies, the Hall coefficient is negative and dominated by the β pocket.
• Oxygen vacancies act as active scattering centers, not merely as electron dopants, and their spatial distribution controls normal-state transport.
  • 证据: In-plane and apical vacancies produce qualitatively different Hall coefficient trends.,The scattering potential from DFT calculations shows strong orbital contrast due to local crystal-field distortions.

研究流程

• model_setup — The correlated multi-orbital model captures the low-energy electronic structure and ARPES Fermiology of superconducting nickelate heterostructures.
  • 方法: DFT+CDMFT-derived correlated multi-orbital quasiparticle model
  • 观察: quasiparticle Fermi surface consists of three pockets (α, β, γ) with distinct orbital characters
• transport_calculation — Multiband compensation is insufficient by itself; oxygen-vacancy scattering selects the transport channels that determine the sign reversal.
  • 方法: T-matrix treatment of oxygen-vacancy scattering; semiclassical Boltzmann transport framework; Ong's geometrical interpretation of weak-field Hall conductivity
  • 观察: rigid-band doping alone does not cause Hall coefficient sign reversal; in-plane vacancies drive the Hall coefficient through zero to positive values; inner-apical vacancies make Hall coefficient more negative
• mechanism_analysis — Pocket-resolved and orbital-selective oxygen-vacancy scattering is the microscopic origin of the Hall coefficient sign reversal, with in-plane vacancies acting as the controlling scatterers.
  • 方法: pocket-resolved and orbital-selective decomposition of Hall conductivity; comparison of inner-apical and in-plane vacancy scattering potentials from DFT
  • 观察: in-plane vacancies selectively suppress the dx2-y2 orbital contribution; the α pocket (dz2) contribution remains nearly unchanged; the sign reversal is driven by the relative suppression of the β pocket contribution