Electrically controllable cyclotron resonance.

Cyclotron resonance (CR) is considered one of the fundamental phenomena in conducting systems. However, Kohn's theorem excludes the possibility of electrically controlling the CR, which significantly limits the scope of research and does not allow to exploit the full application potential of this phenomenon. We demonstrate the breakdown of this theorem in the case of back-gated two-dimensional (2D) electron systems, where the 2D electron sheet is separated from the metallic steering electrode (''back-gate'') by a standard dielectric substrate. The resultant effect is attributed to the retardation of the interaction of 2D electrons and currents with their images in the back-gate. Consequently, we predict that a tremendous shift and narrowing of the CR line can be achieved by varying the electron density or the gate voltage, given the realistic parameters. The effective controllability of CR opens the door for exploring new physics and CR application possibilities.