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  • Open Access

Unconventional Fractional Phases in Multiband Vortexable Systems

Siddhartha Sarkar1,2,*, Xiaohan Wan1,*, Ang-Kun Wu3, Shi-Zeng Lin4,5,†, and Kai Sun1,‡

  • *These authors contributed equally to this work.
  • †Contact author: szl@lanl.gov
  • ‡Contact author: sunkai@umich.edu
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Phys. Rev. Lett. 135, 216501 – Published 20 November, 2025

DOI: https://doi.org/10.1103/jmk4-46tj

Abstract

We study topological flat bands with distinct features that deviate from conventional Landau level behavior. We show that even in the ideal quantum geometry limit, moiré flat band systems can exhibit physical phenomena fundamentally different from Landau levels without lattices. In particular, we find new fractional quantum Hall states emerging from multiband vortexable systems, where multiple exactly flat bands appear at the Fermi energy. While the set of bands as a whole exhibits ideal quantum geometry, individual bands separately lose vortexability, and thus making them very different from a stack of Landau levels. At certain filling fractions, we find fractional states whose Hall conductivity deviates from the filling factor. Through careful numerical and analytical studies, we rule out all known mechanisms—such as fractional quantum Hall crystals or separate filling of trivial and topological bands—as possible explanations. Leveraging the exact solvability of vortexable systems, we use analytic Bloch wave functions to uncover the origin of these new fractional states, which arises from the commensurability between the moiré unit cell and the magnetic unit cell of an emergent effective magnetic field.

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Phys. Rev. Lett. 135, 216501– Published 20 November, 2025
  • Received 20 May 2025
  • Revised 2 September 2025
  • Accepted 28 October 2025
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Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI. Open access publication funded by the Max Planck Society.

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