In this study, we conducted various magnetotransport measurements on Fe 1+y Te 1−x Se x single crystals from which excess iron was sufficiently removed. Our results revealed that crossover from the incoherent to the coherent electronic state and opening of the pseudogap occur at high temperatures (≈ 150 K for x = 0.2). This is accompanied by a more substantial pseudogap and the emergence of a phase with a multi-band nature at lower temperatures (below ≈ 50 K for x = 0.2) before superconductivity sets in. A comparison of these results with those of the as-grown (non-superconducting) samples implies that the coherent state accompanied by the pseudogap is needed for the occurrence of superconductivity in this system. arXiv:1904.13020v1 [cond-mat.supr-con]

Among the Fe-based superconductors, [Formula: see text] is unique in that its crystal structure is the simplest and the electron correlation level is the strongest, and thus it is important to investigate the doping [Formula: see text]-temperature [Formula: see text] phase diagram of this system. However, inevitably incorporated excess Fe currently prevents the establishment of the true phase diagram. We overcome the aforementioned significant problem via developing a new annealing method termed as “Te-annealing” wherein single crystals are annealed under Te vapor. Specifically, we conducted various magnetotransport measurements on Te-annealed superconducting [Formula: see text]. We observed that crossover from the incoherent to the coherent electronic state and opening of the pseudogap occurs at high temperatures ([Formula: see text]150 K for [Formula: see text]). This is accompanied by a more substantial pseudogap and the emergence of a phase with a multi-band nature at lower temperatures (below [Formula: see text] for [Formula: see text]) before superconductivity sets in. Based on the results, the third type electronic phase diagram in Fe-based high-[Formula: see text] superconductors is revealed.

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