Impact of pressure and apical oxygen vacancies on superconductivity in La₃Ni₂O₇

Summary

The bilayer nickelate La₃Ni₂O₇ under pressure has recently emerged as a promising system for high-T_c superconductivity. In this work, we investigate the fate of the superconducting properties in La₃Ni₂O₇ under pressure, focusing on the effects of structural deformation and apical oxygen vacancies. Employing a low-energy effective t-J∥-J⊥ model for the 3d_x2-y2orbitals within the slave-boson mean-field approach, we demonstrate that the pairing strength is significantly enhanced in the high-pressure tetragonal I₄/mmm phase compared to the ambient pressure orthorhombic Amam phase. Furthermore, by simulating random configurations of apical oxygen vacancies, we show that oxygen vacancies suppress both pairing strength and superfluid density. These results underscore the critical role of pressure and oxygen stoichiometry in tuning the SC of La₃Ni₂O₇, providing key insights into optimizing its high-T_c behavior.

Materials

• La₃Ni₂O₇

Methods

• slave-boson mean-field approach
• low-energy effective t-J∥-J⊥ model

Keywords

• pairing strength
• superfluid density
• apical oxygen vacancies
• structural deformation

Highlights

• Demonstrates significant enhancement of pairing strength in high-pressure tetragonal phase.
• Shows that oxygen vacancies suppress pairing strength and superfluid density.

Conclusions

• Pairing strength is significantly enhanced in the high-pressure tetragonal I₄/mmm phase compared to the ambient pressure orthorhombic Amam phase.
• Oxygen vacancies suppress both pairing strength and superfluid density.
• Pressure and oxygen stoichiometry play critical roles in tuning superconductivity of La₃Ni₂O₇.

Main claims

• The superconducting pairing strength and T_c in La₃Ni₂O₇ are significantly enhanced in the high-pressure I₄/mmm phase compared to the ambient-pressure Amam phase.
  • Evidence: SBMF calculations give Δ⊥ = -1.38×10^-2 eV and T_c ≈ 87 K at HP, vs. -2.40×10^-3 eV and 15 K at AP
• Apical oxygen vacancies suppress the superconductivity, reducing both the pairing order parameter and superfluid density.
  • Evidence: Simulations with random vacancies show average Δ⊥ and T_c decreasing with increasing vacancy concentration,Spatial maps show suppression of Δ⊥ at vacancy sites

Workflow

• model_construction — A minimal effective model captures superconductivity.
  • Materials: Bilayer t-J∥-J⊥ model for La₃Ni₂O₇ 3dx2-y2 orbital
  • Methods: Slave-boson mean-field (SBMF) theory; Hopping parameters from DFT
  • Observations: Interlayer pairing Δ⊥ is the dominant order parameter; Δ⊥ is much larger in HP than AP
• effect_of_pressure — Pressure enhances pairing strength and T_c significantly due to increased interlayer superexchange.
  • Materials: Same model with AP and HP parameters
  • Methods: SBMF for pairing amplitudes and T_c
  • Observations: Δ⊥: -2.40×10^-3 eV (AP), -1.38×10^-2 eV (HP); T_c: ≈15 K (AP), ≈87 K (HP); T_c decreases with increasing J∥ for fixed J⊥
• effect_of_apical_oxygen_vacancies — Apical oxygen vacancies suppress superconductivity by reducing interlayer coupling and local electron density.
  • Materials: Bilayer lattice with random apical oxygen vacancies at concentration δ
  • Methods: Real-space SBMF on finite lattice; Introduce zero interlayer hopping/exchange at vacancy sites
  • Observations: Δ⊥ and superfluid density decrease with δ; Local suppression of Δ⊥ near vacancies; T_c drops from ≈0.13t (δ=0) to ≈0.04t (δ=0.15)