Spectroscopic evidence for a first-order transition to a possible orbital Fulde-Ferrell-Larkin-Ovchinnikov state.
basic_science · Level V
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- Record sourced from PubMed, PMID 42120376.
- Also identified by DOI 10.1038/s41467-026-72134-z.
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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-NbSe<sub>2</sub>. 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.