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

Abstract

<jats:p> 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. </jats:p>

Enhanced superconducting pairing strength near a nonmagnetic nematic quantum critical point

“…Single crystals of FeSe 1−x S x and FeSe 1−x Te x for 0 < x ≤ 0.48 were grown by the chemical vapor transport (CVT) technique [22]. Single crystals of FeSe 1−x Te x for 0.52 ≤ x ≤ 0.90 were obtained by the Bridgman method [24]. For the crystals synthesized by the Bridgman method, the Te annealing procedure was applied to minimize the excess Fe [24].…”

“…Single crystals of FeSe 1−x Te x for 0.52 ≤ x ≤ 0.90 were obtained by the Bridgman method [24]. For the crystals synthesized by the Bridgman method, the Te annealing procedure was applied to minimize the excess Fe [24]. The actual Te composition x of FeSe 1−x Te x synthesized by the CVT method was determined for each sample from the c-axis length measured by X-ray diffraction measurements.…”