Superconductor-insulator transitions in infinite-layer nickelates controlled via operando monitored reduction

Area of Science:

• Condensed Matter Physics
• Materials Science
• Superconductivity

Background:

• Nickelates are an emerging class of superconductors with potential for novel electronic properties.
• Achieving continuous control over the superconductor-insulator transition (SIT) in nickelates is crucial for fundamental understanding and applications.
• Existing methods for modulating SIT in nickelates are limited, hindering extensive research.

Purpose of the Study:

• To demonstrate and achieve continuous control over the superconductor-insulator transition (SIT) in infinite-layer nickelate superconductors.
• To explore the relationship between Ni 3d orbital electron occupancy and superconducting properties.
• To investigate the unique characteristics of SIT in nickelates compared to cuprates.

Main Methods:

• Utilized an operando monitored reduction (OMR) method for ultrawide-range continuous modulation of Ni 3d orbital electron occupancy (∼3d⁷ to ∼3d⁹).
• Calibrated 3d occupancy using synchrotron X-ray absorption (XAS) and scanning transmission electron microscopy (STEM) annular bright field (ABF) analysis.
• Modulated SIT further using ionic liquid gating and magnetic field application.

Main Results:

• Demonstrated continuous SIT in infinite-layer nickelate superconductors.
• Nernst effect measurements indicated that superconducting pairing initiates at the onset of the resistive drop, preceding global phase coherence.
• Meissner effect emergence at zero resistance signifies the establishment of global phase coherence.
• Angle-dependent magnetotransport revealed a mix of 2D and 3D superconducting characters, deviating from the canonical 2D SIT model.

Conclusions:

• The study successfully demonstrated continuous control over SIT in nickelates, offering a new pathway for modulating their electronic properties.
• The observed behavior, particularly the early onset of pairing and mixed dimensionality, distinguishes nickelate SIT from cuprates.
• These findings provide a unique perspective on the interplay between structural and electronic phase transitions in infinite-layer nickelates across various parameters.