Theory of cyclotron-resonance absorption

An expression for the cyclotron-resonance power absorption is derived with the help of a projection operator. It is shown that the correct evaluation of this formula requires the summation of an infinite number of terms in order to describe the effects of the scattering interaction to second order. These results are in contradiction with those obtained from some recently proposed theories of this phenomenon. It is then demonstrated that the correct expression for the cyclotron-resonance power absorption is identical to the one obtained through the use of the quantum kinetic equation.