Nonlinear cyclotron resonance of a massless quasiparticle in graphene

We consider the classical motion of a massless quasiparticle in a magnetic field and under a weak electromagnetic radiation with the frequency omega. Due to the nonparabolic linear energy dispersion, the particle responds not only at the frequency omega but generates a broad frequency spectrum around it. The linewidth of the cyclotron resonance turns out to be very broad even in a perfectly pure material which allows one to explain recent experimental data in graphene.