Among the Fe-based superconductors, Fe1+yTe1-xSex 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 (x)-temperature (T) 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 Fe1+yTe1-xSex. We observed that crossover from the incoherent to the coherent electronic state and opening of the pseudogap occurs 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. Based on the results, the third type electronic phase diagram in Fe-based high-Tc superconductors is revealed.
- Fe-based superconductors
- electronic phase diagram
- excess iron
- incoherent to coherent crossover
- magnetotransport measurements