ARPES studies on new types of electron-doped cuprate superconductors

For more than thirty years since the discovery of superconductivity in cuprates, it has been widely agreed that the superconductivity is realized by doping a charge-transfer insulator with charge carriers through chemical substitution. For electron-doped cuprates, however, the recent development of reduction annealing methods has enabled superconductivity for a very small amount of or even without chemical substitution. In this article, we review recent angle-resolved photoemission spectroscopy studies on the new types of electron-doped cuprates with particular emphasis on the effect of reduction annealing. The presented results provide us with renewed insight into the phase diagram and the nature of the pseudogap not only on the electron-doped side but also in the entire doping range including hole doping.