A shadow gap in the over-doped (Ba1-xKx)Fe2As2 compound

Abstract

The electron band around the M point in the $({\text{Ba}_{1-x}}{{\text{K}}_{x}}){\text{Fe}_{2}}{\text{As}_{2}}$ compound, which is completely lifted up above the Fermi level for $x>0.7$ and hence its Fermi surface (FS) disappears, can still play the role of the main pairing resource by exchanging inter-band repulsive interaction with the main hole band ( h1 ) around the $\Gamma $ point. This hidden electron band, which develops the superconducting order parameter (OP) ${{\Delta }_{e}}$ but has no FS, displays a shadow gap feature which is easily detected by various experimental probes such as angle-resolved photoemission spectroscopy (ARPES) and tunneling measurements. We also show that the formation of the nodal gap ${{\Delta }_{\text{nodal}}}$ with ${{A}_{1g}}$ symmetry on another hole pocket ( h2 ) around the $\Gamma $ point with a larger FS is stabilized due to the balance of the inter-band repulsive interactions from the main hole band ( h1 ) with the OP ${{\Delta }_{h1}}={{\Delta }_{+}}$ , and the hidden electron band with the OP ${{\Delta }_{e}}={{\Delta }_{-}}$ .

Keywords

• Fermi surface instability
• iron-based superconductor
• pairing symmetry
• Fe2As2
• nodal gap
• 74.20.-z