Pressure plays an essential role in the induction1 and control2,3 ofsuperconductivity in iron-based superconductors. Substitution of a smallerrare-earth ion for the bigger one to simulate the pressure effects hassurprisingly raised the superconducting transition temperature Tc to the recordhigh 55 K in these materials4,5. However, Tc always goes down after passingthrough a maximum at some pressure and the superconductivity eventually tendsto disappear at sufficiently high pressures1-3. Here we show that thesuperconductivity can reemerge with a much higher Tc after its destruction uponcompression from the ambient-condition value of around 31 K in newly discoverediron chalcogenide superconductors. We find that in the second superconductingphase the maximum Tc is as high as 48.7 K for K0.8Fe1.70Se2 and 48 K for(Tl0.6Rb0.4)Fe1.67Se2, setting the new Tc record in chalcogenidesuperconductors. The presence of the second superconducting phase is proposedto be related to pressure-induced quantum criticality. Our findings point tothe potential route to the further achievement of high-Tc superconductivity iniron-based and other superconductors.
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