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Abrupt change of the superconducting gap structure at the nematic critical point in FeSe1-xSx

Y. Sato, S. Kasahara, T. Taniguchi, X. Xing, Y. Kasahara, Y. Tokiwa, Y. Yamakawa, H. Kontani, T. Shibauchi, and Y. Matsuda, Proc. Natl. Acad. Sci. USA 115, 1227 (2018).

Electronic nematicity that spontaneously breaks the rotational symmetry of the nderlying crystal lattice has been a growing issue in high-temperature uperconductivity of iron pnictides/chalcogenides and cuprates. FeSe1−xSx, in which the nematicity can be tuned by isoelectronic sulfur substitution, offers a fascinating opportunity to clarify the direct relationship between the nematicity and superconductivity. Here, we discover a dramatic change in the superconducting gap structure at the critical concentration of sulfur where the nematicity disappears, i.e., nematic critical point. Our observation provides direct evidence that the orbital-dependent nature of the critical nematic fluctuations has a strong impact on the superconducting pairing interaction.

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