Dynamical regimes of a periodically driven metal and its photoinduced Meissner effect

Periodic driving has emerged as a powerful route to engineer new nonequilibrium phases of matter. In this talk, I will present a field-theoretical model describing a superconductor under a time-periodic modulation, motivated by experiments on light-driven superconductors. Generalizing the model to a O(N)-symmetric one and using a large-N approach, we obtain a nonequilibrium phase diagram featuring a normal state, a superconducting phase oscillating with the drive, and a period-doubled “time-crystalline” superconducting phase. Remarkably, the drive can induce superconductivity even in parameter regimes that are metallic in equilibrium. A Floquet analysis reveals both first- and second-order transitions meeting at a non-Hermitian exceptional point, while numerical simulations show Arnold-tongue–like lobes characteristic of parametric resonance. Finally, I will discuss how both superconducting phases exhibit a finite, period-averaged Meissner effect.