Superconductivity at the border of electron localization and itinerancy

Area of Science:

• Condensed Matter Physics
• Materials Science
• Solid State Chemistry

Background:

• Superconducting states in iron pnictides and chalcogenides are adjacent to anti-ferromagnetic order, suggesting a link between magnetism and unconventional superconductivity.
• Two main theories explain this: one involving localized magnetic moments from strong electron correlations, and another focusing on weakly interacting electrons on nested Fermi surfaces.

Purpose of the Study:

• To investigate the relationship between magnetism and unconventional superconductivity in iron-based superconductors.
• To compare alkaline iron selenide superconductors (lacking Fermi-surface nesting) with iron pnictides to understand pairing mechanisms.

Main Methods:

• Comparative analysis of newly discovered alkaline iron selenide superconductors and established iron pnictide superconductors.
• Application of a strong-coupling approach to evaluate pairing amplitudes in these materials.

Main Results:

• The strong-coupling approach yields similar pairing amplitudes in both alkaline iron selenides and iron pnictides, despite differences in their Fermi surfaces.
• Pairing amplitudes are maximized at the transition between electronic localization and itinerancy.

Conclusions:

• The findings suggest that superconductivity in these iron-based materials may not solely depend on Fermi-surface nesting.
• The results support the idea that superconductivity develops from localized magnetic moments influenced by electron correlations.
• Materials exhibiting characteristics at the boundary of electronic localization and itinerancy are promising candidates for discovering new superconductors.