Infrared spectrum and its implications for the electronic structure of the semiconducting iron selenideK0.83Fe1.53

Electronic Identification of the Parental Phases and Mesoscopic Phase Separation ofKxFe2−ySe2Superconductors

“…Therefore, we could safely deduce a lower limit of the band gap of 40 meV in the semiconducting sample [ Fig. 4(b)], which is consistent with the small indirect gap of about 30 meV deduced from the optical-conductivity data of the semiconducting K 0:8 Fe 2Ày Se 2 [13].…”

“…As illustrated in Fig. 1(a), the resistivity behaviors of these K x Fe 2Ày Se 2 samples are rather versatile, including the insulating and superconducting ones [7], and a semiconducting one that is much less insulating below 100 K as reported before [13]. Interestingly, the resistivity of the superconductor exhibits an insulating behavior above 120 K, while that of the semiconducting compound exhibits an inflexion at 30 $ 50 K. Moreover, the resistivity anomaly near 550 K is present in all the samples, indicating the formation of the vacancy order [7,14].…”

“…Moreover, one of the insulating phases is present in the semiconducting and superconducting compounds, but phase-separated at a mesoscopic scale from the semiconducting and superconducting phases. This mesoscopicscale phase separation is most likely the cause of the complications seen in various earlier measurements [9,[13][14][15]. No band folding that corresponds to the magnetic and vacancy orders in the insulating phases is observed in the electronic structures of the semiconducting and superconducting phases.…”

Theory of two-magnon Raman scattering in alkaline iron selenide superconductors

“…Their locations and regular spacing strongly suggest that the fine structure may come from some Bose modes coupled with the magnetic mode. The most possible mode would be ''phonon'' since the four strongest phonon modes lying at energies of 135, 203, and 265 cm À1 have been found experimentally [43,21]. The present two-magnon theory provides foundations for future microscopic study on ''two-magnon plus phonon'' processes.…”

The orbital characters of low-energy electronic structure in iron-chalcogenide superconductor K x Fe2−y Se2

“…While the parent compounds of most iron-based superconductors are metallic [2][3][4], the parent compound of K x Fe 2−y Se 2 superconductor is found to be either insulating or semiconducting [5][6][7][8][9]. The insulating parental phase even exhibits certain Mott-insulator signatures, and it is phase separated from the superconducting phase in the K x Fe 2−y Se 2 superconductor at a mesoscopic scale [7,10].…”