Origin of a Topotactic Reduction Effect for Superconductivity in Infinite-Layer Nickelates

Area of Science:

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

Background:

• Topotactic reduction using metal hydrides enables access to unusual oxidation states and coordination networks.
• Infinite-layer nickelates are a new class of functional materials with potential superconducting properties.
• The impact of reduction on atomic and electronic structures, critical for superconductivity, is not well understood.

Purpose of the Study:

• To investigate the effects of topotactic reduction on the atomic reconstruction and electronic structure of infinite-layer nickelates.
• To elucidate the role of reduction in modulating nickel-3d orbital polarization and its correlation with superconducting properties.

Main Methods:

• Fabrication of control Nd$_{0.8}$Sr$_{0.2}$NiO$_{2}$ thin films.
• Secondary ion mass spectroscopy (SIMS) to detect hydrogen intercalation.
• X-ray absorption spectroscopy (XAS) to analyze electronic structure and orbital character.

Main Results:

• Absence of reduction-induced hydrogen intercalation confirmed by SIMS.
• XAS revealed dominant Ni 3d$_{x2-y2}$ orbital character and significant linear dichroism in superconducting samples, indicating a Ni single-band nature.
• The asymmetry of Ni 3d orbitals showed a dome-shaped dependence on reduction duration, correlating with superconducting transition temperature (T$_{c}$).

Conclusions:

• Topotactic reduction is crucial for tuning the electronic properties of infinite-layer nickelates.
• Reduction-induced Ni-3d orbital polarization is a key factor influencing superconductivity in these materials.
• This study provides fundamental insights into the mechanism of superconductivity in infinite-layer nickelates.