Self-induced Floquet-Hall effect and multistability of surface plasmons

Floquet engineering offers the tantalizing possibility to dynamically alter material properties on demand using ac fields. In particular, circularly or elliptically polarized electric fields provide optical means for breaking time reversal symmetry in nonmagnetic systems, thereby unlocking time-reversal asymmetric responses such as electrical and thermal Hall conductivities. However, due to the large field strengths often needed to bring about qualitative changes in solid materials, experiments to date have primarily focused on the ultrafast regime. In this work we show that circulating internal electric fields associated with propagating surface plasmons of three dimensional Dirac semimetals mediate a self-induced Floquet-Hall response. When driven at a fixed frequency near resonance, the surface plasmons are subject to a nonlinear feedback whereby the internal field induced Hall conductivity alters the plasmon frequency, which in turn controls the magnitude of the plasmonic internal field. We calculate the time-periodic steady state behavior resulting from this interplay, and show that characteristic nonlinear behaviors including multistability and hysteresis at sufficiently strong external drive amplitudes provide a novel route to revealing Floquet-induced Hall conductivity in Dirac semimetals.