Hierarchical structure of primary and hybridization-induced superconducting correlations in bilayer nickelates

摘要

该研究采用变分蒙特卡洛方法对双层双轨道哈伯德模型进行非微扰计算，揭示了双层层状镍酸盐La₃Ni₂O₇中超导配对的层次结构。研究发现，主要配对相互作用源自Ni 3d(z2)轨道的成键-反成键劈裂，而轨道杂化将超导关联重新分配到3d(x2-y2)通道，尽管该通道自身的内禀配对相互作用很弱。这种配对起源与超导关联来源的区别解释了为何两个轨道通道表现出相当的长程超导关联，且所得s±态对费米面拓扑变化（如α费米面片的消失）具有鲁棒性。该结果调和了此前关于配对机制的不同理论观点，表明超导关联的强度主要由低能态密度的轨道特征决定，而配对相互作用则源于双层结构中的轨道能级分离，突出了轨道杂化在多层层状超导体中稳定超导的关键作用。

材料

• La₃Ni₂O₇

方法

• Variational Monte Carlo (VMC)
• Gutzwiller-Jastrow wave function
• Bogoliubov-de Gennes Hamiltonian
• Stochastic reconfiguration method

关键词

• hierarchical pairing structure
• bonding antibonding splitting
• orbital hybridization
• s± wave superconductivity
• orbital resolved density of states

亮点

• The study establishes a hierarchical structure: primary pairing from bonding-antibonding splitting and hybridization-induced correlations in other channels.
• It reconciles apparently competing theoretical scenarios by distinguishing the origin of pairing from resulting correlations.

结论

• The primary pairing interaction originates from the bonding–antibonding splitting of the Ni 3dz2 orbitals.
• Orbital hybridization redistributes superconducting correlations to the dx2-y2 channel despite its weak intrinsic pairing interaction.
• The resulting s± state is robust against changes in Fermi-surface topology, including the disappearance of the α Fermi pocket.
• Superconducting correlations are governed by the orbital character of the low-energy density of states.

主要论断

• The primary pairing interaction originates from the bonding–antibonding splitting of the Ni 3dz2 orbitals.
  • 证据: Abstract,Full text: The primary pairing interaction originates from the bonding–antibonding splitting of the Ni dz2 orbitals.
• Orbital hybridization redistributes superconducting correlations to the dx2-y2 channel despite its weak intrinsic pairing interaction.
  • 证据: Abstract,Full text: orbital hybridization redistributes superconducting correlations to the dx2-y2 channel despite its weak intrinsic pairing interaction.
• The resulting s± state is robust against changes in Fermi-surface topology, such as the disappearance of the α pocket.
  • 证据: Abstract,Full text: s± state is robust against changes in Fermi-surface topology.

研究流程

• model_setup
  • 材料: La₃Ni₂O₇
  • 方法: bilayer two-orbital Hubbard model; tight-binding parameters from DFT
• variational_Monte_Carlo
  • 方法: Gutzwiller-Jastrow wave function; stochastic reconfiguration optimization
  • 观察: optimized gap parameters; long-range superconducting correlations
• correlation_analysis
  • 方法: orbital-resolved density of states; gap structure in momentum space
  • 观察: comparable correlations in dz2 and dx2-y2 channels; gap structure robust to Fermi surface changes
• interpretation — Primary pairing originates from bonding-antibonding splitting of dz2 orbitals; hybridization induces correlations in dx2-y2 channel.