Absorption of electromagnetic waves in a screened two-dimensional electron system

We studied the absorption of microwave electromagnetic radiation incident normal to a two-dimensional electron system on a dielectric substrate with a metallic back reflector. We have shown that the presence of a back gate strongly modifies the spectrum of plasmon polaritons in such a structure. We observe a transverse plasmon mode which starts from zero frequency at zero magnetic field and follows renormalized cyclotron resonance. This renormalization occurs from the hybridization of plasma modes with Fabry-P\'erot photonic resonances in the substrate, which indicates their transverse nature. Finally, we speculate that the observed modes resemble helicon waves in three-dimensional metals.