Holographic Floquet states II: Floquet condensation of vector mesons in nonequilibrium phase diagram

TL;DR

This paper explores the formation of a Floquet condensate of vector mesons in a strongly driven holographic QCD model, revealing a resonance-driven phase transition and stable non-thermal states with broken symmetries.

Contribution

It introduces the concept of Floquet condensates of vector mesons in a holographic setting, highlighting their stability and relation to resonance phenomena in nonequilibrium phases.

Findings

Resonance with meson excitation energy minimizes the threshold electric field.

A stable Floquet condensate of vector mesons exists even at zero driving field.

The state breaks time translational and reversal symmetries, indicating a non-thermal fixed point.

Abstract

With the aim to reveal universal features of hadronic matter and correlated Dirac insulators in strong AC-electric fields, we study the $\mathcal{N}=2$ supersymmetric QCD with a finite quark mass driven by a rotating electric field $\mathcal{E}_x+i\mathcal{E}_y= E e^{i\Omega t}$. The analysis is done in the holographically dual D3/D7 system in the co-rotating frame, effectively. The nonequilibrium phase diagram is determined from the threshold electric field at which the insulator phase breaks down to a conductive phase due to the AC version of the Schwinger mechanism. The external field induces a rotating current $\mathcal{J}_x + i \mathcal{J}_y = J e^{i\Omega t}$ originating from vacuum polarization and dissipative current in the insulating and conductive phases respectively. Intriguing features are observed as the frequency $\Omega$ approaches resonance with the meson excitation energy $\Omega_{\rm meson}$. There, the threshold minimizes and a condensate of vector mesons with oscillating current exists even in the zero driving field limit. This state, which we call Floquet condensate of vector mesons, is expected to be dynamically stable realizing a non-thermal fixed point that breaks time translational and reversal symmetries. Our finding has many similarities with exciton BEC discussed in solid state systems, where the semiconductor is to be replaced by materials hosting gapped Dirac electrons, e.g. 3D topological insulators or bismuth. Vector meson Floquet condensate may also have implications in the pre-thermalized dynamics in heavy ion collision experiments.