• Accepted Paper

Floquet engineering of a quasiequilibrium superradiant phase transition in Landau polaritons

Wen-Hua Wu, Fuyang Tay, Mengqian Che, Andrey Baydin, Junichiro Kono, and David Hagenmüller

Phys. Rev. Lett. - Accepted 22 October, 2026

DOI: https://doi.org/10.1103/pskw-8xfs

Abstract

Superradiant phase transitions (SRPTs), characterized by photon condensation and macroscopic matter polarization, are forbidden in equilibrium for homogeneous fields by no-go theorems. Here, we show that Floquet driving can circumvent this constraint in a Landau polariton system consisting of a two-dimensional electron gas coupled to a terahertz cavity in a DC magnetic field. An off-resonant AC magnetic field modulates the cyclotron frequency and light–matter coupling strength while leaving the diamagnetic term unchanged, generating an additional DC coupling contribution. This drives the system across a critical threshold into a superradiant phase, characterized by photon condensation and Landau-level polarization in the ground state of the Floquet Hamiltonian. This quasiequilibrium approach offers a route to SRPTs distinct from driven-dissipative schemes.

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