Undoped cuprate superconductors — band superconductors or oxygen-doped Mott-Hubbard superconductors?

Material characterization of superconducting T′-Nd2CuO4 films synthesized by metal organic decomposition

“…Recently, however, we have reported superconductivity with T c over 30 K in the parent compounds, T 0 -RE 2 CuO 4 (RE = Pr, Nd, Sm, Eu, and Gd) [1][2][3]. The origin of the sharp contradiction between the past and our results can be traced to impurity oxygen (O ap ) at the apical site.…”

Evolution of the Electronic State through the Reduction Annealing in Electron-Doped Pr1.3-xLa0.7CexCuO4+δ(x=0.10) Single Crystals: Antiferromagnetism, Kondo Effect, and Superconductivity

“…Finally, it is noted that simple pictures of the band metal without strong electron correlation 6,16) are also able to explain the present results. In the fully reduced ideal state without excess oxygen, localized Cu spins are absent and itinerant electrons bring about superconductivity in the CuO 2 plane.…”

“…That is, the charge-transfer gap between UHB of the Cu3d x 2 −y 2 and the O2p band is collapsed, so that both hole and electron carriers simultaneously emerge at the Fermi level in the parent compounds of the T'-cuprates, carrying SC current. 16) Accordingly, it is speculated that the ideally reduced state of PLCCO with x = 0.10 is a coexistent one of both an electron-doped state of UHB of Cu3d x 2 −y 2 and a hole-doped one of the O2p band, as shown in Fig. 3(b).…”

Optical study of superconductingPr2CuOxwithx≃4

“…In our view, this difference can be related to the absence of an antiferromagnetic phase in PCO. 10,12,21,57 In electron-doped cuprates, the magnetic order induces the pseudogap. With doping, the Neel temperature decreases monotonically leading to a complete suppression of antiferromagnetic order at higher doping accompanied by the disappearance of the pseudogap.…”