Electronic phase diagram of Fe1+yTe1−xSex revealed by magnetotransport measurements

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.