Weak-coupling superconductivity in a strongly correlated iron pnictide

Area of Science:

• Condensed Matter Physics
• Materials Science
• Superconductivity

Background:

• Iron-based superconductors display complex interactions between orbital, spin, and lattice degrees of freedom, influencing their electronic properties and superconductivity.
• The exact mechanism driving superconductivity in these materials remains elusive, with proposed theories involving both orbital and spin channels.

Purpose of the Study:

• To investigate the electronic correlations and superconducting mechanism in nearly optimally doped NaFe0.978Co0.022As, an iron pnictide.
• To elucidate the role of spin-orbit coupling in modifying the electronic band structure and its impact on superconductivity.

Main Methods:

• Utilized optical spectroscopy (OS) and angle-resolved photoemission spectroscopy (ARPES) to probe low-energy electronic properties.
• Performed ab initio band-structure calculations and Eliashberg calculations to model the material's behavior.
• Analyzed orbitally selective electronic correlations and mass enhancement of charge carriers.

Main Results:

• Identified exceptionally strong orbitally selective electronic correlations in NaFe0.978Co0.022As.
• Observed a significant reduction in mass enhancement of itinerant charge carriers near the Γ point, attributed to spin-orbit coupling-induced orbital mixing.
• Demonstrated that the true band structure consistently explains all observed low-energy electronic properties.

Conclusions:

• Superconductivity in this iron pnictide is found to be relatively weak.
• The primary mechanism mediating superconductivity is identified as spin fluctuations.
• Spin-orbit coupling plays a crucial role in modifying electronic correlations and band structure, impacting superconductivity in iron pnictides.