Generally, metals possess Fermi surfaces in momentum space. In a superconducting state, these Fermi surfaces typically disappear as electrons form Cooper pairs. While most superconductors exhibit complete disappearance of Fermi surfaces, recent theoretical proposals have introduced superconductors where sheet-like Fermi surfaces, called Bogoliubov Fermi surfaces, remain. This concept has garnered significant attention in the field.
The iron-based superconductor FeSe1-xSx is considered a promising candidate for exhibiting this phenomenon. However, until now, the anomalous superconducting properties resulting from the presence of Bogoliubov Fermi surfaces have not been thoroughly investigated.
The superconducting properties can be inferred by experimentally measuring the magnetic field penetration depth, which reflects the characteristics of superconductivity.
This study precisely measured the magnetic field penetration depth in the iron-based superconductor FeSe1-xSx. We found that the measured temperature dependence of the penetration depth differs from that of conventional superconductors. Instead, it aligns with theoretical models that assume the presence of Bogoliubov Fermi surfaces.
Furthermore, through systematic measurements of the temperature dependence of the magnetic field penetration depth in samples with introduced defects, we revealed that the results can be qualitatively understood within a framework where the introduction of defects causes the Bogoliubov Fermi surfaces to shrink and eventually disappear.
Papers
Journal: Physical Review Letters
Title: Lifting of Gap Nodes by Disorder in Tetragonal FeSe1-xSx Superconductors
Authors: Takuya Nagashima, Kota Ishihara*, Kumpei Imamura, Masayuki Kobayashi, Masaki Roppongi, Kohei Matsuura, Yuta Mizukami, Romain Grasset, Marcin Konczykowski, Kenichiro Hashimoto, and Takasada Shibauchi*