Dichotomy of superconductivity between monolayer FeS and FeSe

Koshin Shigekawa, Kosuke Nakayama, Masato Kuno, Giao N. Phan, Kenta Owada, Katsuaki Sugawara, Takashi Takahashi, Takafumi Sato

Research output: Contribution to journalArticlepeer-review

21 Citations (Scopus)


The discovery of high-temperature (Tc) superconductivity in monolayer FeSe on SrTiO3 raised a fundamental question: Whether high Tc is commonly realized in monolayer iron-based superconductors. Tetragonal FeS is a key material to resolve this issue because bulk FeS is a superconductor with Tc comparable to that of isostructural FeSe. However, difficulty in synthesizing tetragonal monolayer FeS due to its metastable nature has hindered further investigations. Here we report elucidation of band structure of monolayer FeS on SrTiO3, enabled by a unique combination of in situ topotactic reaction and molecular-beam epitaxy. Our angle-resolved photoemission spectroscopy on FeS and FeSe revealed marked similarities in the electronic structure, such as heavy electron doping and interfacial electron–phonon coupling, both of which have been regarded as possible sources of high Tc in FeSe. However, surprisingly, high-Tc superconductivity is absent in monolayer FeS. This is linked to the weak superconducting pairing in electron-doped multilayer FeS in which the interfacial effects are absent. Our results strongly suggest that the cross-interface electron–phonon coupling enhances Tc only when it cooperates with the pairing interaction inherent to the superconducting layer. This finding provides a key insight to explore heterointerface high-Tc superconductors.

Original languageEnglish
Pages (from-to)24470-24474
Number of pages5
JournalProceedings of the National Academy of Sciences of the United States of America
Issue number49
Publication statusPublished - 2019 Dec 3


  • Angle-resolved photoemission
  • Iron-chalcogenide superconductors
  • Spectroscopy
  • Topotactic synthesis


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