Source capture
Authors Mahiru Seki, Reo Kono, Naotaka Tanaka, Kensei Ushio, Daiki Nakaoka, Masayuki Ochi, Kazuhiko Kuroki, Hirofumi Sakakibara
arXiv / Publisher https://arxiv.org/abs/2605.24565
PDF https://arxiv.org/pdf/2605.24565
Relevance score 5.171
Primary category cond-mat.supr-con
Published 2026-05-26
Research paradigm Theoretical
Sample form Thin Film

Summary

This study constructs a seven-orbital effective model based on first-principles calculations and employs the fluctuation exchange (FLEX) approximation to theoretically analyze the superconductivity of free-standing infinite-layer nickelate Nd0.85Sr0.15NiO2 films under pressure. The results show that the superconducting transition temperature Tc increases monotonically with applied pressure, consistent with recent experimental observations. This enhancement is attributed to the mitigation of excessively strong electronic correlations arising from the extremely low valence state of Ni atoms, leading to a significant reduction in the effective electronic interaction parameter U, which in turn reduces quasiparticle damping and enhances spin-fluctuation-mediated d-wave pairing. Additionally, phonon calculations confirm that the crystal structure remains dynamically stable up to 90 GPa. By comparing models with different U values, the study demonstrates that only a relatively large U (approximately 5.1 eV) can reproduce the experimental trend, while smaller U values lead to premature saturation or even a dome-shaped Tc behavior, thereby supporting the mechanism whereby excessively strong correlations suppress superconductivity in infinite-layer nickelates, and pressure alleviates these correlations to enhance Tc.

Materials

Methods

Keywords

Highlights

  • Seven-orbital effective model constructed from first-principles calculations.
  • Pressure induces a decrease in the effective on-site Coulomb interaction U, leading to enhanced Tc.
  • Phonon calculations confirm dynamical stability of the crystal structure up to 90 GPa.
  • Comparison with experimental data supports the mechanism of correlation mitigation enhancing superconductivity.

Conclusions

  • Superconducting transition temperature Tc increases monotonically with pressure in freestanding infinite-layer nickelate membranes.
  • Enhancement of superconductivity is attributed to mitigation of excessively strong electron correlations due to low valence of Ni.
  • A model with sufficiently large U (≈5.1 eV) is more plausible for infinite-layer nickelates than one with smaller values.

Main claims

  • The seven-orbital model explains the monotonic increase in superconducting transition temperature Tc under pressure observed in experiment.
    • Evidence: FLEX calculation shows eigenvalue lambda (proxy for Tc) increases monotonically with pressure (Fig. 4(b)).,This trend is consistent with experimental Tc increase reported in Ref. [36].
  • The enhancement of Tc is attributed to mitigation of excessively strong electron correlations under pressure.
    • Evidence: Intraorbital interaction U decreases from ≈5.1 eV under pressure (Fig. 4(a)).,Hypothetical models confirm that reducing U (while keeping other parameters fixed) increases lambda.,Smaller U values (4.0, 3.5 eV) give non-monotonic Tc, inconsistent with experiment, supporting that only a large ambient U can explain the data.
  • The crystal structure remains dynamically stable up to 90 GPa.
    • Evidence: Phonon dispersion calculations show no imaginary modes up to 90 GPa (Fig. 1(c)).

Workflow

  • Structural optimization and phonon calculation — Crystal structure remains dynamically stable up to 90 GPa, validating subsequent superconductivity analysis.
    • Materials: Nd0.85Sr0.15NiO2 freestanding membrane
    • Methods: First-principles DFT (Quantum ESPRESSO); Phonon calculations (phonopy)
    • Observations: Lattice parameters decrease under pressure; No imaginary phonon modes up to 90 GPa
  • Band structure and model construction — The seven-orbital model captures essential pressure-induced electronic structure changes.
    • Materials: Nd0.85Sr0.15NiO2 under pressure
    • Methods: Wannierization (wannier90); Construction of seven-orbital effective model
    • Observations: Increase in overall band width; Enhanced three-dimensionality; Self-doping effect: Ni-d occupancy decreases, Fermi pocket enlarges
  • Calculation of interaction parameters — Pressure mitigates excessively strong electronic correlations by reducing U.
    • Materials: Nd0.85Sr0.15NiO2 seven-orbital model
    • Methods: Constrained RPA (RESPACK)
    • Observations: Intraorbital interaction U_d decreases from ≈5.1 eV at ambient to lower values under pressure; Hund's coupling J remains nearly constant; Ratio U/J decreases significantly
  • Superconductivity analysis via FLEX — Monotonic enhancement of Tc under pressure is reproduced only with realistic U≈5.1 eV, supporting the mechanism that pressure alleviates excessive correlations to boost superconductivity.
    • Materials: Seven-orbital model with various U values
    • Methods: Fluctuation exchange (FLEX) approximation; Eliashberg equation (d-wave)
    • Observations: Eigenvalue lambda monotonically increases with pressure for U=5.1 eV; Hypothetical models with only U or J changed confirm U reduction drives lambda increase; Smaller U (4.0, 3.5 eV) leads to premature saturation or dome-shaped Tc