Pressure-induced insulator-metal transition and the pathway towards superconductivity in alkaline iron selenide compounds

The newly discovered iron selenide superconductors, with superconducting transition temperatures of 32 K at ambient pressure and 48 K at high pressure, prominently feature an insulating “245 phase” in its microstructure . Although a series of distinctive properties have been confirmed in these materials, there exists one puzzle vital to the understanding of superconductivity, viz. how the insulating 245 phase connects to the