Magnetless Approaches to Break and Engineer Reciprocity with 2D Materials
Two-dimensional materials offer new and exciting possibilities to break time-reversal symmetry and manipulate it at the nanoscale in the absence of magnetic bias. For instance, the ultrafast field effect in graphene can be exploited to modulate in space and time the electrical properties of this material, imparting linear or angular momentum to the waves propagating within the system. This approach has been applied to propose (i) plasmonic isolators and nonreciprocal leaky-wave antennas at terahertz frequencies; and (ii) low-loss photonic isolators that use spatiotemporally modulated graphene as a perturbation to engineer nonreciprocal coupling between photonic states. Other possibility relies on applying a longitudinal DC voltage to nanostructured 2D materials, inducing drifting electrons that interact with the collective charge oscillations of the supported surface plasmons and enforce different plasmon wavelength for opposite propagation directions. In this talk, we will discuss the advantages and challenges — including limitations associated to loss and modulation speed — of these approaches and how they can be applied to realize quasi optimal nonreciprocal devices. We envision that the exotic properties of 2D materials will pave the way to magnetic-free, fully-integrated and CMOS-compatible nonreciprocal components with wide applications in communication systems, sensing, imaging, and on-chip networks.