Bose-Einstein condensation superconductivity induced by disappearance of the nematic state

Takahiro Hashimoto, Yuichi Ota, Akihiro Tsuzuki, Tsubaki Nagashima, Akiko Fukushima, Shigeru Kasahara, Yuji Matsuda, Kohei Matsuura, Yuta Mizukami, Takasada Shibauchi, Shik Shin, Kozo Okazaki

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30 Citations (Scopus)


The crossover from the superconductivity of the Bardeen-Cooper-Schrieffer (BCS) regime to the Bose-Einstein condensation (BEC) regime holds a key to understanding the nature of pairing and condensation of fermions. It has been mainly studied in ultracold atoms, but in solid systems, fundamentally previously unknown insights may be obtained because multiple energy bands and coexisting electronic orders strongly affect spin and orbital degrees of freedom. Here, we provide evidence for the BCS-BEC crossover in iron-based superconductors FeSe1xSx from laser-excited angle-resolved photoemission spectroscopy. The system enters the BEC regime with x = 0.21, where the nematic state that breaks the orbital degeneracy is fully suppressed. The substitution dependence is opposite to the expectation for single-band superconductors, which calls for a new mechanism of BCS-BEC crossover in this system.

Original languageEnglish
Article numbereabb9052
JournalScience Advances
Issue number45
Publication statusPublished - Nov 4 2020
Externally publishedYes

ASJC Scopus subject areas

  • General


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