Evolution of local structure and superconductivity in CaFe₂As₂

Area of Science:

• Condensed Matter Physics
• Materials Science
• Solid State Chemistry

Background:

• The 122 class of materials, particularly iron arsenides, are known for their unconventional superconductivity.
• Understanding the interplay between structure, electronic properties, and superconductivity is crucial for designing new superconducting materials.

Purpose of the Study:

• To investigate the local structural parameter evolution in CaFe2As2 and its Co-doped superconducting counterpart.
• To correlate these structural changes with electronic properties and their implications for superconductivity.

Main Methods:

• Extended X-ray Absorption Fine Structure (EXAFS) studies were performed on CaFe2As2 and CaFe1.9Co0.1As2.
• Analysis focused on spectral functions near Fe K- and As K-absorption edges.
• Local structural parameters, including bond lengths, were determined.

Main Results:

• Co substitution enhances Fe contributions near the Fermi level, particularly at low temperatures.
• Fe-As and Fe-Fe bond lengths evolve with temperature across the magneto-structural transition in the parent compound.
• Similar structural evolution trends were observed in the superconducting Co-doped material, despite the absence of a magneto-structural transition.

Conclusions:

• Doping induces structural evolution towards critical behavior or strong nematic fluctuations.
• These findings suggest a significant role for doping-induced structural and electronic changes in enabling superconductivity in these materials.