Site specific spin dynamics in BaFe2As2: tuning the ground state by orbital differentiation

TL;DR

This study uses Electron Spin Resonance to explore how orbital differentiation influences superconductivity in BaFe2As2, revealing that increased Fe 3d orbital anisotropy correlates with the suppression of magnetic order and the emergence of superconductivity.

Contribution

It demonstrates that orbital anisotropy and localization in Fe 3d bands are key factors in the transition from magnetic order to superconductivity in BaFe2As2.

Findings

Orbital anisotropy increases as SDW phase is suppressed.

Orbital localization occurs independently of chemical substitution.

Enhanced Fe 3d orbital symmetry favors superconductivity.

Abstract

The role of orbital differentiation on the emergence of superconductivity in the Fe-based superconductors remains an open question to the scientific community. In this investigation, we employ a suitable microscopic spin probe technique, namely Electron Spin Resonance (ESR), to investigate this issue on selected chemically substituted BaFe$_{2}$As$_{2}$ single crystals. As the spin-density wave (SDW) phase is suppressed, we observe a clear increase of the Fe 3$d$ bands anisotropy along with their localization at the FeAs plane. Such an increase of the planar orbital content interestingly occurs independently on the chemical substitution responsible for suppressing the SDW phase. As a consequence, the magnetic fluctuations combined with the resultant particular symmetry of the Fe 3$d$ bands are propitious ingredients to the emergence of superconductivity in this class of materials.