Heterostructuring as Gateway to Electron Doping of Nickelate Superconductors

Summary

This study proposes a novel route to electron doping in nickelate superconductors through heterostructuring. First-principles calculations reveal that upon inserting wide-bandgap insulating layers of LaXO₃ (X = Al, Ga, Sc) into La₂NiO₄, the additional (LaO)⁺ layers act as electron donors, releasing carriers into the Ni-3d orbitals and thereby achieving disorder-free electron doping of Ruddlesden–Popper nickelates. This doping naturally places La₂NiO₄:La₂AlO₄ in the optimal regime for dx2−y2-wave superconductivity, with 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. The strategy circumvents the disorder typically introduced by conventional chemical doping, and is equally applicable to other nickelates such as La₃Ni₂O₇, offering a viable scheme for comprehensively mapping the electron-doping phase diagram of nickelates and extending the approach to other transition metal oxide systems.

Materials

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

Methods

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

Keywords

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

Highlights

• 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.

Conclusions

• 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.

Main claims

• Wide-band-gap insulator intercalation provides a disorder-free electron doping route in Ruddlesden-Popper nickelates.
  • Evidence: "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.
  • Evidence: "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.
  • Evidence: "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).

Workflow

• Heterostructure Design — Intercalating LaXO₃ (X=Al, Ga, Sc) layers into La₂NiO₄ introduces extra (LaO)+ layers that act as electron donors.
  • Materials: La₂NiO₄; LaAlO₃; LaGaO₃; LaScO₃
  • Methods: 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.
  • Materials: La₂NiO₄:La₂AlO₄; La₂NiO₄; La₃Ni₂O₇:La₃Al₂O₇
  • Methods: Density functional theory (PBE-GGA); Projector augmented wave (PAW) method in VASP; FP-(L)APW+lo basis in WIEN₂k
  • Observations: 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.
  • Materials: La₂NiO₄:La₂AlO₄
  • Methods: DFT+DMFT; Constrained random phase approximation (cRPA) for interaction parameters; Continuous-time quantum Monte Carlo (CT-QMC) solver; Wannier projection with Wannier90 and Wien2Wannier
  • Observations: 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.
  • Materials: La₂NiO₄:La₂AlO₄
  • Methods: Dynamical vertex approximation (DΓA); Fluctuation exchange (FLEX); Dynamical cluster approximation (DCA); Bethe-Salpeter equation for T_c; One-band Hubbard model from Wannier projection
  • Observations: 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.
  • Materials: La₂NiO₄:La₂AlO₄
  • Methods: Self-consistent phonon (SCPH) calculations; Ab initio molecular dynamics (AIMD) with machine-learned force fields; Convex hull construction from DFT energies
  • Observations: 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