Cyclotron resonance overtones and near-field magnetoabsorption via terahertz Bernstein modes in graphene

2D electron systems subjected to a perpendicular magnetic field absorb electromagnetic radiation via the cyclotron resonance (CR). In this presentation, we will discuss a qualitative breach of this well-known behavior in graphene. Our study of the THz photoresponse reveals a resonant burst at the main overtone of the CR, drastically exceeding the signal due to the ordinary CR. In accordance with the developed theory, the photoresponse dependencies on the magnetic field, doping level, and sample geometry suggest that the origin of this anomaly lies in the near-field magnetoabsorption facilitated by the Bernstein modes, ultra-slow magnetoplasmonic excitations reshaped by nonlocal electron dynamics. These modes are characterized by a diverging plasmonic density of states that strongly amplifies the radiation absorption. Our results show that the radiation absorption via nonlocal collective modes can facilitate a strong photoresponse, a behavior potentially useful for IR and THz technology.