First-Principles Evidence for Strongly Correlated Superconductivity Driven by Structural Variations in La₃Ni₂O₇

摘要

本研究通过第一性原理模拟，结合约束随机相位近似和从头算分子动力学，系统分析了La₃Ni₂O₇在超导压力范围内的电子关联行为。结果显示，伴随结构相变，Ni的e_g轨道有效在位排斥显著增强，归因于轨道局域化与竞争屏蔽通道（特别是spacer层La能带）之间的动态平衡。该增强区域与实验观测的右三角形超导穹顶高度吻合，且在18 GPa处关联强度达到峰值，对应最高超导临界温度。有限温度模拟进一步澄清了结构相图边界，而Ac₃Ni₂O₇的计算则确认A位阳离子在压力驱动电子关联演化中的关键作用。这些结果直接揭示了结构变化如何通过调控电子关联强度驱动非常规超导电性。

材料

• La₃Ni₂O₇
• Ac₃Ni₂O₇

方法

• DFT
• cRPA
• AIMD
• Wannier downfolding

关键词

• electronic correlations
• structural phase transition
• screening
• a site cation substitution

亮点

• First ab initio evidence linking enhanced correlations to the right-triangular superconducting dome in La₃Ni₂O₇.
• Uses cRPA to show that screening from La spacer bands dominates in the high-pressure limit, reducing correlations.
• Predicts that Ac₃Ni₂O₇ may exhibit superconductivity near ambient pressure but with lower maximal T_c.

结论

• The effective on-site repulsion in the Ni eg bands is significantly enhanced within the superconducting pressure range, peaking at 18 GPa.
• This enhancement arises from a competition between orbital localization and competing screening from La spacer bands.
• The superconducting region in the P-T phase diagram coincides with the region of enhanced correlations, closely tracking the critical temperature.
• Ac₃Ni₂O₇ confirms the crucial role of the A-site cation in shaping pressure-driven evolution of correlations.
• Finite-temperature AIMD simulations clarify the structural phase diagram and origin of the right-triangular dome.

主要论断

• Enhanced electronic correlations coincide with the right-triangular superconducting region in La₃Ni₂O₇ phase diagram
  • 证据: From abstract: 'superconducting region in the La₃Ni₂O₇ phase diagram coincides with a region of enhanced electronic correlations, which show a close correspondence with the critical temperature'
• At low pressures, enhanced correlations due to structural transition; at high pressures, screening from La 5d bands reduces correlations
  • 证据: From text: 'pressure-driven competition between orbital localisation, reduced octahedral distortions, and band splitting… and increased screening from the spacer La bands',From abstract: 'We attribute this increase to an interplay between orbital localisation and competing screening channels'

研究流程

• density_functional_theory_calculations — Structural phase transition from orthorhombic to tetragonal at ≈10 GPa
  • 材料: La₃Ni₂O₇; Ac₃Ni₂O₇
  • 方法: DFT with PBE functional; structural optimization at fixed pressures
  • 观察: lattice parameters; bond angles
• constrained_random_phase_approximation — Effective on-site repulsion increases with pressure due to orbital localization and reduced screening
  • 材料: Optimized structures
  • 方法: cRPA for effective interactions; Wannier downfolding
  • 观察: screened Coulomb interactions U, U', J
• ab_initio_molecular_dynamics_simulations — Finite-temperature phase boundaries determined; right-triangular superconducting dome correlates with enhanced correlations
  • 材料: La₃Ni₂O₇
  • 方法: AIMD in NPT ensemble
  • 观察: time-averaged lattice constants; bond angles