Superconductivity in Sr-doped La₃Ni₂O₇ thin films

Area of Science:

• Materials Science
• Condensed Matter Physics
• Solid State Chemistry

Background:

• Recent discoveries highlight ambient pressure superconductivity in compressively strained La3Ni2O7 thin films.
• The phase diagram of heterovalent doping in these materials is crucial for advancing superconductivity research but remains underexplored.

Purpose of the Study:

• To investigate superconductivity in strontium (Sr2+)-doped La3-xSrxNi2O7 thin films.
• To explore the impact of heterovalent doping on the superconducting properties and phase diagram of La3Ni2O7.

Main Methods:

• Thin film synthesis of Sr2+-doped La3Ni2O7.
• Electrical transport measurements to determine superconducting transition temperature (Tc), critical current (Jc), and upper critical fields (μ0Hc).
• Scanning transmission electron microscopy (STEM) to analyze structural properties and oxygen vacancy distribution.

Main Results:

• Superconductivity was observed in La3-xSrxNi2O7 films with a Tc following an incomplete dome-like profile.
• Optimally doped films exhibited a Tc of ~42 K, high Jc (>1.4 kA cm-2 at 2 K), and significant upper critical fields (μ0Hc,∥(0) = 83.7 T, μ0Hc,⟂(0) = 110.3 T).
• STEM revealed planar oxygen vacancies and elongated out-of-plane Ni-O bonds, attributed to compressive strain, potentially weakening interlayer coupling.

Conclusions:

• Heterovalent doping with Sr2+ introduces superconductivity in La3Ni2O7 thin films, expanding the known superconducting phase space.
• The observed structural modifications under strain, including planar oxygen vacancies and altered Ni-O bond lengths, influence superconducting properties.
• Further research into strain engineering and doping strategies is warranted for optimizing high-Tc materials.