Pressure-Driven Evolution of Electronic and Magnetic Correlations in Bilayer Nickelate La₃Ni₂O₇

Summary

Using a combination of density functional theory, constrained random phase approximation, and dynamical mean-field theory, we systematically investigate the evolution of electronic and magnetic correlations in the bilayer nickelate La₃Ni₂O₇ under pressure. Our calculations show that hydrostatic pressure enhances interlayer hopping and the bare superexchange energy scale, while reducing the relative correlation strength U/W, driving the system overall towards an itinerant state. Crucially, a clear orbital-selective evolution is observed: the Ni dx²-y² orbital becomes increasingly itinerant, whereas the Ni dz² orbital retains strong localization; pressure enhances their hybridization, greatly amplifying the Kondo screening effect of itinerant electrons on the localized magnetic moments. Consequently, the effective magnetic exchange coupling that mediates pairing is suppressed in the high-pressure regime, indicating that the monotonic decrease of the superconducting transition temperature under high pressure arises from Kondo screening overwhelming the superexchange interaction, and thus providing a self-consistent microscopic explanation for the dome-shaped superconducting phase diagram of La₃Ni₂O₇.

Materials

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Methods

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Keywords

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Highlights

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Conclusions

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Main claims

• Hydrostatic pressure enhances interlayer hopping and the bare superexchange energy scale, while reducing the relative correlation strength U/W.
  • Evidence: cRPA results show monotonic increase of t_perp and 4t2/U, and continuous decrease of U/W with pressure.
• The Ni dx2-y2 state becomes increasingly itinerant under pressure, whereas the Ni dz2 orbital retains a more localized character.
  • Evidence: DMFT spectral functions show stronger renormalization of dz2 band.,Hybridization function of dx2-y2 is strongly enhanced near EF with pressure.
• Pressure‑enhanced hybridization amplifies the Kondo‑like screening of localized dz2 moments by itinerant dx2-y2 electrons.
  • Evidence: DMFT local spin susceptibility decreases with pressure.,Extracted Kondo scale T_K increases by a factor ≈4 from 14.1 to 90 GPa.
• The effective interlayer magnetic exchange coupling J_eff is suppressed in the high‑pressure regime.
  • Evidence: TB₂J calculations show peak in |J_⊥| near 45 GPa and subsequent reduction at higher pressures.,Orbital magnetic moments, especially dx2-y2, are quenched at high pressure.
• The monotonic decrease of T_c at high pressures is driven by the dominance of Kondo screening over superexchange interactions, explaining the dome‑shaped superconducting phase diagram.
  • Evidence: Simultaneous increase of T_K and decrease of J_eff above the optimal pressure.,T_K reaches ≈400 K at 90 GPa, indicating efficient screening of moments needed for pairing.

Workflow

• DFT_and_Wannier_Construction — The low‑energy physics is reliably captured by a two‑orbital (dx2-y2, dz2) Wannier model.
  • Materials: La₃Ni₂O₇
  • Methods: DFT with WIEN₂k (FP-LAPW); PBE-GGA exchange-correlation; Wannier90 MLWF
  • Observations: Ni 3d orbitals dominate near EF; dz2 band nearly occupied and narrow; dx2-y2 band more dispersive; Excellent agreement between DFT and Wannier interpolation
• cRPA_Parameter_Derivation — Hydrostatic pressure enhances interlayer hopping and bare superexchange, but simultaneously reduces the relative correlation strength U/W.
  • Materials: La₃Ni₂O₇
  • Methods: Constrained Random Phase Approximation (cRPA) with projector method; Downfolding onto Ni 3d Wannier subspace
  • Observations: Screened U non‑monotonic, peaks around 30–60 GPa (≈2.9 eV) then decreases to ≈2.5 eV; Hund’s J nearly constant ≈0.65 eV; Bonding bandwidth W monotonically increases from ≈1.6 to 2.4 eV; U/W decreases continuously; Interlayer hopping t_perp and bare superexchange scale 4t2/U increase monotonically
• DFT+DMFT_Calculations — The dx2-y2 orbital becomes increasingly itinerant under pressure, dramatically amplifying the Kondo screening of the localized dz2 moments.
  • Materials: La₃Ni₂O₇
  • Methods: Charge‑self‑consistent DFT+DMFT (EDMFT code); CT‑HYB impurity solver; Maximum entropy analytic continuation
  • Observations: Orbital‑selective renormalization: dz2 band strongly renormalized, dx2-y2 more dispersive; dx2-y2 hybridization function strongly enhanced at EF with pressure; Local spin susceptibility χ_loc suppressed with pressure; Curie‑Weiss slope nearly constant → effective moment weakly pressure‑dependent; Weiss temperature intercept gives Kondo scale T_K that rises from ≈0.01 to ≈0.04 eV (≈ 116–464 K)
• Magnetic_Exchange_Calculations — The effective interlayer antiferromagnetic exchange is non‑monotonic and weakened at high pressure by itinerancy‑induced moment quenching.
  • Materials: La₃Ni₂O₇
  • Methods: Spin‑polarized DFT (ABACUS); TB₂J Green’s‑function method; Heisenberg model mapping
  • Observations: dz2 orbital carries the dominant magnetic moment, which decreases gradually; dx2-y2 moment strongly suppressed above 60 GPa; Nearest‑neighbour interlayer exchange J_⊥ is antiferromagnetic and non‑monotonic, peaking near 45 GPa (~ −7 meV) then suppressed; dx2-y2 channel contribution to J_⊥ much smaller than dz2 channel
• Synthesis_and_Interpretation — The dome‑shaped superconducting phase diagram arises from the competition between pressure‑enhanced superexchange and Kondo screening; at high pressure, excessive screening suppresses the pairing glue, causing the monotonic T_c decrease.
  • Methods: Comparison of cRPA, DMFT, and TB₂J trends; Estimation of Kondo scale T_K from local susceptibility
  • Observations: Bare superexchange 4t2/U increases monotonically, but effective exchange J_eff decreases at high pressure; Kondo screening scale T_K grows rapidly at high pressure; Local moments become increasingly screened above the optimal T_c region