STM/S study on the role of Arsenic in Iron-based Superconductivity at Atomic Scale

We use scanning tunneling microscopy /spectroscopy to investigate the role of Arsenic in superconducting Ba0.4K0.6Fe2As2 by directly breaking and repairing the local Fe-As structure. After the up-As-layer peeled away, the tunneling spectrum of the exposed Fe surface reveals a shallow incoherent gap, indicating a severe suppression of superconductivity without As covering. When an As-dimmer is placed on the same Fe surface, a localized topographic feature is formed due to p-d orbital hybridization and the superconducting coherent peaks recover locally with the superconducting gap size exactly the same as the Fe-layer with a complete As-coverage. These observations unravel the Fe-As interactions on an atomic scale and imply its essential roles in the Fe-based superconductivity.