Tunable bound states in the continuum in active metasurfaces of graphene disk dimers

Bound states in the continuum (BICs) in metasurfaces have lately attracted a great deal of attention stemming from their inherent (formally) divergent Q factors, which lead to an enhancement of light-matter interaction in two-dimensional geometries. However, the development of plausible means to actively manipulate them remains a major challenge. The use of graphene layers has recently been suggested, employed either as a substrate or a coating that modifies the dielectric environment of the metasurface. Here, instead, we propose to exploit graphene disk dimers supporting in-plane plasmons directly as active meta-atoms in a square array. We prove analytically that both the emergence of a BIC and its Q factor can be tuned in an active manner by applying a different external potential to each of the disks in the dimer, thus being formally equivalent to engineering the disk diameters in a passive, geometrically-dependent manner. Moreover, we propose an approach to mitigate the effect of the inherent losses of graphene plasmons based on exploiting the collective behavior of the array, which is achieved by adjusting the lattice parameter so that the wavelength of the BIC mode lies closer to the Rayleigh anomaly.