Characteristic two-dimensional Fermi surface topology of high-Tc iron-based superconductors.

Unconventional Cooper pairing originating from spin or orbital fluctuations has been proposed for iron-based superconductors. Such pairing may be enhanced by quasi-nesting of two-dimensional electron and hole-like Fermi surfaces (FS), which is considered an important ingredient for superconductivity at high critical temperatures (high-T_c). However, the dimensionality of the FS varies for hole and electron-doped systems, so the precise importance of this feature for high-T_c materials remains unclear. Here we demonstrate a phase of electron-doped CaFe₂As₂ (La and P co-doped CaFe₂As₂) withT_c=45 K, which is the highest Tc found for the AEFe₂As₂ bulk superconductors (122-type; AE = Alkaline Earth), possesses only cylindrical hole- and electron-like FSs. This result indicates that FS topology consisting only of two-dimensional sheets is characteristic of both hole- and electron-doped 122-type high-T_c superconductors. [ABSTRACT FROM AUTHOR]