Reversible symmetry breaking of BIC graphene plasmons for tunable mid-infrared absorption

We use symmetry breaking to create switchable absorption peaks in mid-infrared (MIR) graphene metamaterials. We consider a structure consisting of graphene nanoribbons in contact with a gold grating. The unit cell of the untuned device is symmetric and supports both a bright and dark plasmon; the latter is also known as a BIC (bound state in the continuum) mode. We break symmetry by dynamically tuning the chemical potential of one of two graphene nanoribbons per unit cell. We show numerically that the BIC mode couples to the continuum, turning on an absorption peak. As the tuning increases, the two modes spatially flip and concentrate in a single nanoribbon. By controlling the relative chemical potential of two ribbons, we can control the wavelength of the switchable absorption peak.