Floquet engineering of antihelical edge states and related transport properties in a modified Kane-Mele model

We investigate optically modulated antihelical edge states (AHESs) and two-terminal transport in the modified Kane-Mele (MKM) model irradiated with off-resonant circularly polarized light (CPL). Our results show that tuning the light intensity and polarization transforms the original AHESs into a variety of photo-dressed edge states. The resulting spin-dependent Hall conductance, which is governed by the Berry curvature, reflects bulk topology even in the presence of gapless states, achieved through non-quantized Hall responses. When CPL is locally applied to the scattering region of a two-terminal zigzag graphene nanoribbon, spin-resolved conductance pathways can be selectively switched due to edge-state transitions. This behavior is visualized through calculations of time-averaged local bond current. Notably, replacing CPL with a staggered electric field configuration fully suppresses transmission due to the bandgap effect induced by this field, thereby realizing an optoelectronic transistor. Our findings highlight how Floquet engineering in the MKM model facilitates topological control of edge states and transport, thus paving a pathway for light-controlled quantum devices.