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Flux-Floquet Instability in Fluctuating Superconductors

Marios H. Michael1,2,*, Duilio De Santis3,4, Eugene A. Demler4, and Patrick A. Lee5

  • *Contact author: marios.michael@mpsd.mpg.de
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Phys. Rev. X 16, 031055 – Published 31 August, 2026

DOI: https://doi.org/10.1103/tq9r-g727

Abstract

In the past decade, photoinduced superconductinglike behaviors have been reported in a number of materials driven by intense pump fields. Of particular interest is the high-Tc cuprate YBa2Cu3O6+x (YBCO), where such effect has been reported up to the so-called pseudogap temperature T*∼300–400  K. In a recent tour-de-force experiment, a transient magnetic field which is proportional to and in the same direction of an applied field has been observed outside the sample, suggestive of flux exclusion due to the Meissner effect. In this paper, we present an alternative interpretation of these experiments based on a mechanism that we term the flux-Floquet instability of the sine-Gordon (SG) model. We take as our premise the model of preformed Cooper pairs in the pseudogap phase. Starting from the local superconducting order parameter in equilibrium, we introduce an extended SG model to describe the dynamics of the relative phase between the layers of a bilayer. We demonstrate that a combination of external magnetic field and strong terahertz drive used in experiments by Fava et al. results in a novel Floquet instability in the model. This instability leads to currents at the edges of the bilayer formed by defects or grain boundaries, with the current flowing in the opposite direction of the equilibrium screening current, producing a giant paramagnetic magnetization in the same direction as the applied field. We show how this scenario can fit most of the available data. To the extent that this model can account for the data, we conclude that the experiments have the important consequence of revealing the presence of local pairing in the pseudogap phase. While the bulk of this paper addresses the experiment on YBCO, our results reveal a new instability in the SG equation that is of fundamental interest, with potential applications such as providing a mechanism for generating large magnetic fields at ultrafast timescales in Josephson devices.

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Superconductivity normally disappears when thermal fluctuations disrupt the coordinated motion of bound electron pairs, leaving it unclear whether these pairs survive far above the transition temperature in high-temperature superconductors. We show that intense terahertz light dramatically amplifies the small magnetic response of these local electron pairs by triggering a flux-Floquet instability. Our theoretical framework explains recent experimental observations of transient magnetic response in driven cuprate superconductors, where we predict that edge currents generate a strong transient paramagnetic field aligned with an applied static field. Consequently, our results support the presence of short-range electron pairing within the pseudogap phase well above the superconducting transition temperature. More broadly, we anticipate that this instability mechanism will provide a route for generating large ultrafast magnetic responses in other quantum many-body systems, such as extended Josephson junctions, excitonic insulators, and cold atoms coupled to artificial gauge fields.

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Phys. Rev. X 16, 031055– Published 31 August, 2026
  • Received 12 March 2025
  • Revised 27 April 2026
  • Accepted 15 July 2026
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