Evolution from incoherent to coherent electronic states and its implications for superconductivity inFeTe1−xSex

Abstract

We have performed systematic angle-resolved photoemission spectroscopy (ARPES) of iron-chalcogenide superconductor FeTe 1−x Se x (0 x 0.45) to elucidate the electronic states relevant to the superconductivity. While the Fermi-surface shape is nearly independent of x, we found that the ARPES spectral line shape shows prominent x dependence. A broad ARPES spectrum characterized by a small quasiparticle weight at x = 0, indicative of incoherent electronic states, becomes progressively sharper with increasing x, and a welldefined quasiparticle peak appears around x = 0.45 where bulk superconductivity is realized. The present result suggests the evolution from incoherent to coherent electronic states and its close relationship to the emergence of superconductivity.

Experimental observation of incoherent-coherent crossover and orbital-dependent band renormalization in iron chalcogenide superconductors

“…As we are preparing our manuscript, a similar report 31 also addressed the evolution from incoherent to coherent electronic states in FeSe x Te 1−x , consistent with our conclusion. In addition to 31 , our first discovery on the orbital dependent band renormalization provides a deeper understanding of the nature of the strong correlations in multiple orbital systems such as Fe 1+y Se x Te 1−x .…”

Incoherent-coherent crossover and the pseudogap in Te-annealed superconductingFe1+yTe1−xSexrevealed by magnetotransport measurements

“…In other words, the existence of the coherent state with the pseudogap is a prerequisite for the occurrence of superconductivity. The importance of the coherent electronic state for the emergence of superconductivity has been inferred by ARPES measurements [5,6]. Here, we verified, using transport measurements, that the incoherent to coherent transition and opening of the pseudogap always take place in the superconducting Fe 1+y Te 1−x Se x samples at the doping(x)dependent characteristic temperature T * * R H (or T * ρ ab ) above T c .…”

“…On the other hand, the evolution from incoherent to coherent electronic states with increasing Se doping, i.e., by increasing x, in this Fe 1+y Te 1−x Se x system was observed by angle-resolved photoemission spectroscopy (ARPES) [5,6]. That is, a broad ARPES spectrum for both the hole and electron bands near Γ and the M point, respectively, for samples with x ≤ 0.2, which is indicative of incoherent electronic states, has been shown to progressively change to sharper ones, thereby indicating coherent electronic states, for the samples with x ≥ 0.4.…”

Spectral properties of transition metal pnictides and chalcogenides: Angle-resolved photoemission spectroscopy and dynamical mean-field theory

“…Coherence-incoherence crossover in FeTe 1−x Sex (reprinted with permission from Ref [132],. copyright ©(2014) by The American Physical Society): (a) Schematic phase diagram of FeTe 1−x Sex derived from Ref [133,134,135]…”