Heterostructuring as Gateway to Electron Doping of Nickelate Superconductors

摘要

该研究提出通过异质结构实现镍酸盐超导体电子掺杂的新途径。第一性原理计算表明，在La₂NiO₄中插入宽带隙绝缘层LaXO₃（X=Al, Ga, Sc）时，额外的(LaO)⁺层作为电子供体向Ni-3d轨道释放载流子，从而实现对Ruddlesden-Popper型镍酸盐的无序电子掺杂。该掺杂使La₂NiO₄:La₂AlO₄自然处于d_(x²-y²)波超导的最佳区域，动态顶点近似、涨落交换和动态团簇近似等多体方法预测其超导临界温度超过50 K，最高可达127 K。这种策略避免了传统化学掺杂引入的无序问题，且同样适用于La₃Ni₂O₇等镍酸盐，为全面探索镍酸盐电子掺杂相图及拓展至其他过渡金属氧化物体系提供了可行方案。

材料

• La₂NiO₄:La₂AlO₄
• La₂NiO₄:La₂GaO₄
• La₂NiO₄:La₂ScO₄
• La₃Ni₂O₇:La₃Al₂O₇

方法

• DFT
• DMFT
• DΓA
• FLEX
• DCA
• cRPA
• SCPH
• AIMD

关键词

• electron doping
• heterostructuring
• nickelate superconductors
• wide band gap insulator intercalation
• d wave superconductivity
• disorder free doping
• ruddlesden popper nickelates

亮点

• Proposes a disorder-free route to electron doping via heterostructuring, circumventing the challenges of substitutional doping.
• Predicts high-T_c d-wave superconductivity (50–127 K) in La₂NiO₄:La₂AlO₄ using multiple many-body methods (DΓA, FLEX, DCA).
• Demonstrates the versatility of the approach by applying it to La₃Ni₂O₇ and suggesting extension to cuprates and ruthenates.
• Provides structural stability analysis (phonon, molecular dynamics) confirming the viability of the proposed heterostructures.

结论

• Intercalating wide-band-gap insulating layers such as LaXO₃ (X=Al, Ga, Sc) into La₂NiO₄ achieves disorder-free electron doping of Ruddlesden-Popper nickelates.
• La₂NiO₄:La₂AlO₄ is naturally in the optimal region for dx2-y2-wave superconductivity with T_c exceeding 50 K (up to 127 K).
• The same electron-doping concept is applicable to La₃Ni₂O₇ and other RP-phase oxides.
• The heterostructuring route avoids chemical disorder and provides a symmetry-preserving strategy for accessing the electron-doped side of nickelate phase diagrams.

主要论断

• Wide-band-gap insulator intercalation provides a disorder-free electron doping route in Ruddlesden-Popper nickelates.
  • 证据: "When intercalating wide-band-gap insulating layers such as LaXO₃ (X=Al, Ga, Sc) into La₂NiO₄, the extra (LaO)+ layers act as electron donors" (Abstract).,"First-principles calculations… confirm significant charge transfer from the La(Al,Ga,Sc)O₃-derived blocks into NiO₂ layers, driving Ni toward d9 configurations" (Introduction).,"Bader charge analysis and Mulliken population analysis… consistent with a Ni+ state and a d9 configuration" (SM XIII).
• La₂NiO₄:La₂AlO₄ is a dx2-y2-wave superconductor with T_c exceeding 50 K at ambient pressure.
  • 证据: "Many-body methods—including dynamical vertex approximation, fluctuation exchange, and dynamical cluster approximation—predicting a superconducting critical temperature exceeding 50 K and reaching as high as 127 K" (Summary).,"DA… yields T_c values of 53 and 62 K for n=0.87 and n=0.95… FLEX… 103 K and 115 K… DCA… 127 K" (Superconductivity section).,"The leading eigenvalue… indicates dx2-y2-wave pairing symmetry" (SM VIII).
• The electron doping strategy is broadly applicable to other RP nickelates and transition-metal oxides.
  • 证据: "The same concept also allows us to electron dope La₃Ni₂O₇" (Abstract).,"For La₃Ni₂O₇, we constructed an La₃Ni₂O₇:La₃Al₂O₇ superlattice… DFT bands with a pronounced downward shift of the Ni-d orbitals, corresponding to an electron-doping" (DFT bands section).,"The approach is not at all restricted to nickelates. It is widely applicable to… cuprates such as La₂CuO₄ and ruthenates such as Sr₂RuO₄" (Conclusions).

研究流程

• Heterostructure Design — Intercalating LaXO₃ (X=Al, Ga, Sc) layers into La₂NiO₄ introduces extra (LaO)+ layers that act as electron donors.
  • 材料: La₂NiO₄; LaAlO₃; LaGaO₃; LaScO₃
  • 方法: Intercalation of wide-band-gap insulating layers into Ruddlesden-Popper phases; Formal valence counting and ionic considerations
• DFT Electronic Structure Calculation — DFT confirms that La₂AlO₄ intercalation electron-dopes the NiO₂ planes, driving Ni toward a d9 configuration.
  • 材料: La₂NiO₄:La₂AlO₄; La₂NiO₄; La₃Ni₂O₇:La₃Al₂O₇
  • 方法: Density functional theory (PBE-GGA); Projector augmented wave (PAW) method in VASP; FP-(L)APW+lo basis in WIEN₂k
  • 观察: Ni-dx2-y2 occupancy increases from 0.56 (undoped) to 0.87 (doped) in DMFT; Fermi surface becomes quasi-single-band with nearly full dz2 and half-filled dx2-y2; Charge transfer confirmed by Bader and Mulliken analysis
• Correlation Treatment with DMFT — Electron correlations preserve a metallic state dominated by the Ni-dx2-y2 orbital, with La pockets serving as an electron reservoir.
  • 材料: La₂NiO₄:La₂AlO₄
  • 方法: DFT+DMFT; Constrained random phase approximation (cRPA) for interaction parameters; Continuous-time quantum Monte Carlo (CT-QMC) solver; Wannier projection with Wannier90 and Wien2Wannier
  • 观察: Ni-dx2-y2 occupation 0.87 in La-4f,5d,Ni-3d model; Effective mass m*/m ≈ 3.1; La-5d pockets cross Fermi level but are decoupled from Ni-d bands
• Superconductivity Prediction via Many-Body Methods — La₂NiO₄:La₂AlO₄ is a d-wave superconductor with T_c exceeding 50 K, likely higher than infinite-layer nickelates.
  • 材料: La₂NiO₄:La₂AlO₄
  • 方法: Dynamical vertex approximation (DΓA); Fluctuation exchange (FLEX); Dynamical cluster approximation (DCA); Bethe-Salpeter equation for T_c; One-band Hubbard model from Wannier projection
  • 观察: Leading pairing symmetry: dx2-y2-wave; DΓA: T_c = 53–62K; FLEX: T_c = 103–115K; DCA: T_c = 127K
• Structural Stability Assessment — The proposed heterostructure is dynamically and thermodynamically stable.
  • 材料: La₂NiO₄:La₂AlO₄
  • 方法: Self-consistent phonon (SCPH) calculations; Ab initio molecular dynamics (AIMD) with machine-learned force fields; Convex hull construction from DFT energies
  • 观察: No imaginary phonon modes; Stable MD trajectories with no bond breaking; Heterostructure lies on the convex hull of the La-Ni-Al-O pseudo-quaternary phase diagram