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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-Tc). However, the dimensionality of the FS varies for hole and electron-doped systems, so the precise importance of this feature for high-Tc materials remains unclear. Here we demonstrate a phase of electron-doped CaFe2As2 (La and P co-doped CaFe2As2) withTc=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-Tc superconductors. [ABSTRACT FROM AUTHOR]

We report the results of photoemission spectroscopy on the potassium concentration (x) dependence of Kx picene films on graphite. The results show a systematic shift of a whole valence band and the appearance of a clear Fermi edge for a certain value of x, with additional structures at higher binding energies. Observed spectral evolutions are reminiscent to those of doped C60, implying that the Kx picene film has multiple phases depending on the K concentration. Appearance of a clear Fermi edge, in contrast to multilayer Kx picene films on Au, SiO2, and Ag(111) substrates, where no clear Fermi edges are observed, suggests that the emergence of the metallic states for Kx picene films depends on the specific molecular orientations in the films on different substrates. [ABSTRACT FROM AUTHOR]

We studied the electronic structure of Ca10(Pt4As8)(Fe2-xPtxAs2)5 for two platinum concentrations with different Tc using ARPES. From the carrier number estimated from the areas of FS sheets, we found that the Pt substitution induces electron doping into the Fe2As2 layers (effectively two electrons per Pt atom). In addition, we found that the FS nesting condition in x = 0.25 is stronger than that in x = 0.42, indicating close correlation between the FS nesting and Tc. [ABSTRACT FROM AUTHOR]