Abstract
The orbital Fulde-Ferrell-Larkin-Ovchinnikov (orb-FFLO) state has lately emerged as an exotic dissipationless state, but a thermodynamic demonstration, which is key for its establishment, has been lacking. Here, we reveal a first-order quantum phase transition in the tunneling spectroscopy under an in-plane magnetic field on multilayer 2H-NbSe2. The transition manifests itself as a sudden enhancement of the superconducting gap with prominent hysteresis by sweeping the in-plane magnetic field well below the upper critical field. Such a first-order transition quickly disappears once the magnetic field tilts away from the in-plane direction by about one degree, and it depends sensitively on disorder. Furthermore, we obtain a comprehensive phase diagram of the phase transition as a function of magnetic field, temperature, and the sample thickness. These observed behaviors can be reproduced by the theory that considers the energetics between a uniform Ising superconductor and the orb-FFLO state.
Similar content being viewed by others
Acknowledgements
We thank Ignacio Gutierrez for helpful discussions. D. Z. and Q.-K. X. acknowledge financial support from the Ministry of Science and Technology of China (2022YFA1403100); Q.-K. X. acknowledges financial support from National Natural Science Foundation of China (Grant No. 52388201); D. Z. acknowledges financial support from National Natural Science Foundation of China (Grants No. 12361141820, No. T2425009, No. 12274249) and Innovation Program for Quantum Science and Technology (Grant No. 2021ZD0302400); H. L. acknowledge financial support from National Key Research and Development Program of China (Grant No. 2024YFA1409001) and National Natural Science Foundation of China (Grants No. 12374037); A. F. M. gratefully acknowledges the Swiss National Science Foundation for financial support; M. L. acknowledges financial support from the Swiss National Science Foundation through the Ambizione program and National Natural Science Foundation of China (Grant No. 92565102); K.W. and T.T. acknowledge support from the JSPS KAKENHI (Grant Numbers 20H00354 and 23H02052) and World Premier International Research Center Initiative (WPI), MEXT, Japan.
Author information
Authors and Affiliations
Corresponding authors
Ethics declarations
Competing interests
The authors declare no competing interests.
Additional information
Publisher’s note Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.
Supplementary information
Rights and permissions
Open Access This article is licensed under a Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License, which permits any non-commercial use, sharing, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if you modified the licensed material. You do not have permission under this licence to share adapted material derived from this article or parts of it. The images or other third party material in this article are included in the article’s Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the article’s Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this licence, visit http://creativecommons.org/licenses/by-nc-nd/4.0/.
About this article
Cite this article
Cao, Z., Liao, M., Yan, H. et al. Spectroscopic evidence for a first-order transition to a possible orbital Fulde-Ferrell-Larkin-Ovchinnikov state. Nat Commun (2026). https://doi.org/10.1038/s41467-026-72134-z
Received:
Accepted:
Published:
DOI: https://doi.org/10.1038/s41467-026-72134-z
