Pairing mechanism and superconductivity in 1313 phase La₃Ni₂O₇

摘要

通过密度泛函理论结合动力学平均场理论（DFT+DMFT）和随机相位近似（RPA）系统研究了1313相La₃Ni₂O₇的电子结构和超导机制。DMFT计算表明，单层子系统呈近绝缘态，其中dz²轨道表现出莫特物理，而三层子系统保持金属性，超导主要源于后者，且其Ni-e_g轨道相对于块体La₄Ni₃O₁₀处于空穴掺杂状态。基于DMFT导出的低能有效哈密顿量，RPA分析给出三层子系统内为s±波配对对称性。与块体La₄Ni₃O₁₀相比，1313相超导转变温度显著降低的原因有两个：一是空穴掺杂减弱了配对强度；二是单层子系统作为弱连接层，将相邻的三层超导层构成S-N-S约瑟夫森结，抑制了层间相位相干，从而进一步降低全局转变温度。综合结果表明，RP相La₃Ni₂O₇家族中的高温超导应归属于2222相而非1313相。

材料

• 1313La₃Ni₂O₇

方法

• DFT+DMFT
• random phase approximation (RPA)

关键词

• s± pairing
• hole doping
• interlayer josephson coupling
• mott physics
• trilayer subsystem

亮点

• Establishes that the high-T_c phase in the La₃Ni₂O₇ family is the 2222 bilayer structure, not the 1313 phase.
• The S-N-S Josephson junction model explains suppressed phase coherence in hybrid phases.

结论

• The single-layer subsystem in 1313La₃Ni₂O₇ exhibits nearly insulating behavior with Mott physics for the d_z2 orbital, while the trilayer subsystem remains metallic and hosts superconductivity with s± pairing.
• The reduced T_c compared to bulk La₄Ni₃O₁₀ is due to hole doping in the trilayer subsystem and weak interlayer Josephson coupling across the single-layer spacer.

主要论断

• The monolayer subsystem exhibits nearly insulating behavior with the 3d_z2 orbital showing Mott physics, while the trilayer subsystem remains metallic and is primarily responsible for superconductivity.
  • 证据: DMFT calculations reveal that the monolayer subsystem exhibits a nearly insulating state, with the d_z² orbital displaying Mott physics, while the trilayer subsystem remains metallic and is primarily responsible for superconductivity
• RPA analysis yields an s±-wave pairing symmetry within the trilayer subsystem.
  • 证据: Based on the low-energy effective Hamiltonian derived from DMFT, RPA analysis yields an s±-wave pairing symmetry within the trilayer subsystem.
• The significantly reduced T_c in 1313 phase arises from hole doping weakening pairing strength and the monolayer subsystem acting as weak-link layers forming S-N-S Josephson junctions, suppressing interlayer phase coherence.
  • 证据: the significantly reduced superconducting transition temperature in the 1313 phase arises from two factors: first, hole doping weakens the pairing strength; second, the monolayer subsystem acts as a weak-link layer, forming S-N-S Josephson junctions between adjacent trilayer superconducting layers, which suppresses interlayer phase coherence and further lowers the global transition temperature.

研究流程

• DFT+DMFT calculation — SC primarily resides in the TL subsystem; SL subsystem is a nearly insulating bad metal.
  • 材料: 1313 phase La₃Ni₂O₇ at 20 GPa
  • 方法: density functional theory plus dynamical mean-field theory (DFT+DMFT)
  • 观察: pronounced band renormalization; SL subsystem: nearly insulating bad metal, 3d_z2 orbital shows Mott physics; TL subsystem: metallic, holes doped relative to bulk La₄Ni₃O₁₀
• effective model construction — Renormalized model captures low-energy physics with s± pairing tendency.
  • 材料: TL subsystem of 1313La₃Ni₂O₇
  • 方法: tight-binding model derived from DFT+DMFT
  • 观察: renormalized bandwidth 2.1 eV; interlayer hopping reduced; Fermi surface consists of multiple pockets
• RPA analysis of superconductivity — The TL subsystem exhibits s±-wave pairing symmetry.
  • 材料: effective TL two-orbital model
  • 方法: random phase approximation (RPA)
  • 观察: spin susceptibility dominated by nesting between α and β pockets; leading pairing instability in s±-wave channel
• analysis of Tc suppression — Two factors suppress T_c: hole doping in TL and weak Josephson coupling between TL subsystems.
  • 材料: 1313La₃Ni₂O₇ compared to bulk La₄Ni₃O₁₀
  • 方法: comparison of doping and Josephson coupling
  • 观察: hole doping reduces pairing strength; weak intertrilayer hopping leads to S-N-S Josephson junction