Characteristic two-dimensional Fermi surface topology of high-T(c) 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 CaFe(2)As(2) (La and P co-doped CaFe(2)As(2)) with T(c) = 45 K, which is the highest T(c) found for the AEFe(2)As(2) 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.