A Unified Understanding of the Experimental Controlling of the Tc of La₃Ni₂O₇

摘要

该论文基于先前提出的有效dx2-y2轨道双层t-J∥-J⊥模型，结合第一性原理计算输入的模型参数，通过奴隶玻色子平均场和密度矩阵重正化群方法，统一解释了通过氧化学计量、元素替代、压力或应变调控La₃Ni₂O₇超导转变温度（T_c）的一系列实验。模型发现，由于dx2-y2轨道接近四分之一填充，其T_c调控行为与空穴掺杂的过掺杂铜氧化物类似。在掺杂依赖性上，系统呈现粒子-空穴不对称性：空穴掺杂使系统更过掺杂而抑制T_c，电子掺杂则相反，这解释了氧过量或Ca/Sr替代La导致的T_c抑制以及氧化学计量调控中的“半穹顶”行为。在相互作用依赖性上，T_c随层间反铁磁超交换相互作用J⊥变化，这解释了Sm/Nd替代La增强体材料T_c、体材料T_c-压力呈“直角三角形”关系以及薄膜中压应变增强T_c的实验现象。与弱耦合理论（T_c主要依赖于态密度）和dz2轨道主导的配对机制（T_c与dz2空穴密度成比例）相比，该模型提供了更自然统一的解释。论文进一步提出，通过不引入无序的电子掺杂（如用更高价元素替代La）可提高T_c。

材料

• La₃Ni₂O₇
• La₂PrNi₂O₇

方法

• Slave-boson mean-field theory (SBMF)
• Density matrix renormalization group (DMRG)
• First-principles DFT calculations

关键词

• overdoped cuprates analogy
• particle hole asymmetry
• interlayer superexchange j⊥
• hole doping suppresses tc
• electron doping enhances tc
• half dome behavior

亮点

• Provides a unified understanding of diverse experiments (oxygen stoichiometry, element substitution, pressure, strain) within a single d-orbital bilayer model.
• Predicts that electron doping without inducing disorder (e.g., substituting La with higher-valence elements) can enhance T_c.

结论

• T_c is determined by the pairing temperature in the overdoped regime, increasing with filling fraction and interlayer superexchange J⊥.
• Hole doping suppresses T_c by moving the system further into the overdoped regime, while electron doping enhances T_c.
• Pressure and strain dependence of T_c are mediated by changes in J⊥, explaining the dome-shaped pressure-T_c relation and the enhancement under compressive strain.
• The half-dome behavior in oxygen stoichiometry tuning arises from competing effects of electron doping and oxygen vacancy disorder.

主要论断

• The T_c of La₃Ni₂O₇ is controlled by the filling fraction of the dx²-y² orbital and the interlayer antiferromagnetic superexchange J⊥, analogous to hole-doped overdoped cuprates.
  • 证据: SBMF and DMRG calculations show T_c increases with filling fraction and J⊥ in the overdoped regime
• Hole doping (via over-oxidization or Ca/Sr substitution) suppresses T_c, while electron doping enhances T_c.
  • 证据: Calculations show particle-hole asymmetry: hole doping decreases DOS and T_c; electron doping increases DOS and T_c; consistent with experimental half-dome and substitution experiments
• The enhancement of T_c by Nd/Sm substitution of La, the right-triangle pressure dependence, and the enhancement by compressive strain are all due to variation of J⊥ with experimental conditions.
  • 证据: DFT calculations show J⊥ increases with Nd substitution, with pressure up to 30 GPa then decreases, and with compressive strain; SBMF calculates corresponding T_c that matches experimental trends

研究流程

• model_development — A minimal model for La₃Ni₂O₇ superconductivity.
  • 材料: first-principles DFT calculations
  • 方法: effective dx²-y² orbital bilayer t-J∥-J⊥ model
  • 观察: model captures near quarter-filling of dx²-y² orbital
• theoretical_calculations — T_c behavior analogous to hole-doped overdoped cuprates.
  • 材料: model parameters
  • 方法: slave-boson mean field theory; DMRG
  • 观察: T_c is controlled by filling fraction and interlayer superexchange J⊥
• comparison_with_experiments — Unified understanding of T_c control experiments.
  • 材料: experimental data on T_c control
  • 方法: systematic variation of parameters to match experiments
  • 观察: model reproduces half-dome oxygen stoichiometry dependence, enhancement by Nd/Sm substitution, right-triangle pressure dependence, and compressive strain enhancement
• comparison_with_alternative_theories — Strong-coupling dx²-y² model provides more natural understanding.
  • 材料: RPA and d_z²-orbital dominated pairing calculations
  • 方法: same model parameters for RPA
  • 观察: RPA fails to explain most experiments; d_z² mechanism also fails