Structural modifications in strain-engineered bilayer nickelate thin films

Area of Science:

• Materials Science
• Condensed Matter Physics
• Solid-State Chemistry

Background:

• High-temperature superconductivity discovered in La₃Ni₂O₇ under pressure and strain.
• Understanding the atomic and electronic structure interplay is crucial for superconductivity.
• Specific nickel-oxygen bond modifications driving superconductivity remain unclear.

Purpose of the Study:

• To investigate the atomic-scale structural evolution of La₃Ni₂O₇ thin films under biaxial strain.
• To correlate structural modifications with superconductivity.
• To isolate the effects of specific structural motifs on superconductivity.

Main Methods:

• Utilized multislice electron ptychography (MEP) for picometer-resolution structural analysis.
• Examined La₃Ni₂O₇ thin films with varying biaxial strains.
• Resolved both cation and oxygen sublattices to study atomic bond evolution.

Main Results:

• Identified lifting of crystalline symmetry via nickel-oxygen octahedral distortions under compressive strain.
• Observed in-plane lattice compression as a common factor in bulk and thin film superconductivity.
• Developed a theoretical framework to analyze coupled structural distortions.

Conclusions:

• Compressive strain-induced symmetry lifting in nickel-oxygen octahedra is key for superconductivity.
• In-plane lattice compression is a unifying feature for La₃Ni₂O₇ superconductivity.
• Superconducting states suppress local t_2g orbital mixing by raising octahedral symmetry.