Pressure has an essential role in the production1 and control2,3 of superconductivity in iron-based superconductors. Substitution of a large cation by a smaller rare-earth ion to simulate the pressure effect has raised the superconducting transition temperature Tc to a record high of 55 K in these materials4,5. In the same way as Tc exhibits a bell-shaped curve of dependence on chemical doping, pressure-tuned Tc typically drops monotonically after passing the optimal pressure1,2,3. Here we report that in the superconducting iron chalcogenides, a second superconducting phase suddenly re-emerges above 11.5 GPa, after the Tc drops from the first maximum of 32 K at 1 GPa. The Tc of the re-emerging superconducting phase is considerably higher than the first maximum, reaching 48.0–48.7 K for Tl0.6Rb0.4Fe1.67Se2, K0.8Fe1.7Se2 and K0.8Fe1.78Se2.
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We thank I. I. Mazin, W. Bao, and T. Xiang for discussions and J. S. Schilling for the help with the alternating-current susceptibility technique. This work in China was supported by the NSCF, 973 projects, and Chinese Academy of Sciences. This work in the USA was supported as part of the EFree, an Energy Frontier Research Center funded by the US Department of Energy, Office of Science, Office of Basic Energy Sciences (DOE-BES). The High Pressure Collaborative Access Team (HPCAT) is supported by CIW, CDAC, UNLV and LLNL through funding from the DOE-NNSA, the DOE-BES and the NSF. The Advanced Photon Source (APS) is supported by the DOE-BES.
The authors declare no competing financial interests.
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Sun, L., Chen, XJ., Guo, J. et al. Re-emerging superconductivity at 48 kelvin in iron chalcogenides. Nature 483, 67–69 (2012). https://doi.org/10.1038/nature10813
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