Impact of multiband effects on non-Fermi-liquid transport phenomena in bilayer nickelates

摘要

本研究采用多轨道紧束缚模型分析薄层双层镍酸盐La₃Ni₂O₇中的非费米液体输运现象，重点考察多带效应对霍尔系数的影响。通过格林函数方法推导了包含准量子度量（qQM）项的严格霍尔系数公式，发现该qQM项的温度依赖性在强关联多带体系中至关重要。计算表明，Ni d₂²轨道自旋涨落导致更强的准粒子阻尼，而Ni d_x²_-y²轨道形成冷点。La₃Ni₂O₇中霍尔系数的显著温度依赖源于空穴带正贡献与电子带负贡献的竞争，qQM项使得低温下正霍尔系数增强，并解释了实验中观察到的T线性电阻率和霍尔系数随温度降低而上升的行为。此外，该qQM项对描述Nernst系数及其他涉及速度二阶导数的输运现象也起关键作用。研究揭示了自旋涨落诱导的轨道选择性重整化在非费米液体输运中的核心机制，为理解该体系的奇异输运性质提供了理论框架。

材料

• La₃Ni₂O₇

方法

• Multi-orbital tight-binding model
• Fluctuation-exchange approximation (FLEX)
• Green's function method
• Linear response theory

关键词

• non fermi liquid transport
• t linear resistivity
• hall coefficient
• quasi quantum metric
• cold spots
• spin fluctuations
• orbital selective renormalization

亮点

• First derivation of a rigorous formula for the Hall coefficient including many-body qQM effects in strongly correlated multiband systems.
• Explains both T-linear resistivity and the increasing positive Hall coefficient at low temperatures in thin-film bilayer nickelates.

结论

• Spin fluctuations cause stronger quasiparticle damping in the Ni dz2 orbital, leading to cold spots on the Ni dx2-y2 orbital.
• Derived a rigorous formula for the Hall coefficient incorporating the many-body quasi-quantum metric (qQM) term; the temperature dependence of the qQM term is crucial for determining RH.
• The temperature dependence of RH arises from competition between positive hole band and negative electron band contributions; the qQM term enhances positive RH at low temperatures, explaining experimental observations.

主要论断

• The temperature dependence of the Hall coefficient in La₃Ni₂O₇ is dominated by the quasi-quantum metric term, which becomes significant due to strong orbital-dependent quasiparticle damping.
  • 证据: Derived rigorous formula for Hall coefficient with qQM term; calculations show qQM term enhances positive contribution at low T
• Spin fluctuations cause stronger quasiparticle damping in the d_z² orbital, while dx²-y² forms cold spots, leading to orbital-selective transport.
  • 证据: FLEX self-energy calculations show larger ImΣ for d_z² than dx²-y²; cold spots appear on α and β FSs where dx²-y² weight dominates
• The competition between hole and electron pockets, together with the qQM term, explains the observed T-linear resistivity and positive Hall coefficient increasing at low temperatures.
  • 证据: Calculated ρxx shows linear T dependence; R_H positive and increases at low T; matches experimental data from Ref. 1,4

研究流程

• model_construction — Realistic tight-binding model for thin-film La₃Ni₂O₇.
  • 材料: thin-film La₃Ni₂O₇
  • 方法: multiorbital tight-binding model from DFT; modification to match ARPES
  • 观察: three Fermi surfaces: α, β, γ; cold spots near X point
• flex_calculation — Orbital-selective quasiparticle damping due to spin fluctuations.
  • 材料: tight-binding model
  • 方法: fluctuation exchange approximation; self-energy calculation
  • 观察: spin fluctuations cause larger quasiparticle damping in d_z² orbital; dx²-y² forms cold spots
• transport_calculation — Non-Fermi-liquid transport phenomena reproduced.
  • 材料: self-energy from FLEX
  • 方法: linear response theory with qQM formula for Hall coefficient
  • 观察: T-linear resistivity; positive Hall coefficient that increases at low T; negative Nernst coefficient