Connection between ambient-pressure and pressure-induced superconducting phases in alkaline iron selenide superconductors

A unique platform for investigating the correlation between the antiferromagnetic (AFM) and superconducting (SC) states in high temperature superconductors is created by the discovery of alkaline iron selenide superconductors which are composed of an AFM insulating phase and a SC phase separated spatially. Our previous studies showed that pressure can fully suppress the superconductivity of ambient-pressure superconducting phase (SC-I) and AFM order simultaneously, then induce another superconducting phase (SC-II) at higher pressure. Consequently, the connection between the two superconducting phases becomes an intriguing issue. In this study, on the basis of observing pressure-induced reemergence of superconductivity in Rb0.8Fe2-ySe2-xTex (x=0, 0.19 and 0.28) superconductors, we find that the superconductivity of the SC-I and SC-II phases as well as the AFM ordered state can be synchronously tuned by Te doping and disappear together at the doping level of x=0.4. We propose that the two superconducting phases are connected by the AFM phase, in other words, the state of long-ranged AFM order plays a role in giving rise to superconductivity of the SC-I phase, while the fluctuation state of the suppressed AFM phase drives the emergence of SC-II phase. These results comprehensively demonstrate the versatile roles of AFM states in stabilizing and developing superconductivity in the alkaline iron selenide superconductors.