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  • Open Access

Fate of the Fermi Surface Coupled to a Single-Wave-Vector Cavity Mode

Bernhard Frank1, Michele Pini2,3,*, Johannes Lang4, and Francesco Piazza2,3

  • *Contact author: michele.pini@uni-a.de
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Phys. Rev. Lett. 136, 143403 – Published 10 April, 2026

DOI: https://doi.org/10.1103/t4xb-6x3z

Abstract

The electromagnetic field of standing-wave or ring cavities induces a spatially modulated, infinite-range interaction between atoms in an ultracold Fermi gas, with a single wavelength comparable to the Fermi length. This interaction has no analog in other systems of itinerant particles and has so far been studied only in the regime where it is attractive at zero distance. Here, we fully solve the problem of competing instabilities of the Fermi surface induced by single-wavelength interactions. We find that while the density-wave (superradiant) instability dominates on the attractive side, it is absent for repulsive interactions, where the competition is instead won by nonsuperradiant superfluid phases at low temperatures, with fermion pairs forming at both vanishing and finite center-of-mass momentum. Moreover, even in the absence of such symmetry-breaking instabilities, the Fermi surface exhibits a peculiar anisotropic deformation. We estimate this full phenomenology to be within reach of dedicated state-of-the-art experimental setups.

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Phys. Rev. Lett. 136, 143403– Published 10 April, 2026
  • Received 16 May 2025
  • Revised 18 December 2025
  • Accepted 12 March 2026
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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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