Signatures of Amorphous Shiba State in FeTe<sub>0.55</sub>Se<sub>0.45</sub>
The iron-based superconductor FeTe<sub>0.55</sub>Se<sub>0.45</sub> is a peculiar material: it hosts surface states with a Dirac dispersion, is a putative topological superconductor hosting Majorana modes in vortices, and has an unusually low Fermi energy. The superconducting state is generally characterized by three gaps in different bands, with the homogeneous, spatially extended Bogoliubov excitations─in this work, we uncover evidence that it is instead of a very different nature. Our scanning tunneling spectroscopy data show several peaks in the density of states above a full gap, and by analyzing their spatial and junction-resistance dependence, we conclude the peaks above the first one are not coherence peaks from different bands. Instead, comparisons with our simulations indicate they originate from generalized Shiba states that are spatially overlapping. This can lead to an amorphous state of Bogoliubov quasiparticles, reminiscent of impurity bands in semiconductors. We discuss the origin and implications of this new state.
Authors
- Andreas Kreisel (ORCID: https://orcid.org/0000-0003-3028-377X)
- Koen M. Bastiaans (ORCID: https://orcid.org/0000-0002-2871-4166)
- Jens Paaske (ORCID: https://orcid.org/0000-0002-8087-591X)
- Brian M. Andersen (ORCID: https://orcid.org/0000-0002-9786-7553)
- S.-I. Lee (ORCID: https://orcid.org/0009-0001-4930-1037)
- Doo‐Hee Cho (ORCID: https://orcid.org/0000-0002-0939-3731)
- Milan P. Allan (ORCID: https://orcid.org/0000-0002-5437-1945)
- Damianos Chatzopoulos (ORCID: https://orcid.org/0000-0002-7443-9820)
- Jinwon Lee (ORCID: https://orcid.org/0000-0002-6075-5101)
- Genda Gu (ORCID: https://orcid.org/0000-0002-2025-5444)
Institutions
- Leiden University (NL)
- University of Copenhagen (DK)
- Yonsei University (KR)
- Brookhaven National Laboratory (US)
- Center for NanoScience (DE)
- Quantum Devices (United States) (US)
- FZU ‒ Institute of Physics of the Academy of Sciences of the Czech Republic (CZ)
- Yukhnovskii Institute for Condensed Matter Physics of the National Academy of Sciences of Ukraine (UA)
- Munich Center for Quantum Science and Technology (DE)
- Ludwig-Maximilians-Universität München (DE)
Publication Details
- Journal
- Nano Letters
- Published
- 2025-02-12
- DOI
- https://doi.org/10.1021/acs.nanolett.4c05650
- Citations
- 2
- Primary Topic
- Iron-based superconductors research
- Type
- article
- Field-Weighted Citation Impact
- 0.85
Funders
- U.S. Department of Energy
- National Research Foundation
- Universiteit Leiden
- Technische Universiteit Delft
- Yonsei University
- National Research Foundation of Korea
- Brookhaven National Laboratory
- H2020 European Research Council