  Recent cyclotron resonance experiments in n-type CdS at ultra-high magnetic
fields have revealed a pronounced maximum of the electron cyclotron mass as a
function of temperature. In order to interpret these data, we calculate the
magneto-absorption spectra of polarons in n-CdS using the arbitrary-coupling
approach. We show that in high magnetic fields the polaron effects beyond the
weak-coupling approximation clearly reveal themselves in the magneto-optical
absorption even at relatively small values of the Froehlich coupling constant.
In particular, those effects result in a non-monotonous behaviour of the
cyclotron mass as a function of temperature. We extend the theory to take into
account a combined effect of several scattering mechanisms on the
magneto-absorption spectra. The extended theory allows us to interpret
quantitatively the experimentally observed behaviour of the cyclotron mass in
CdS.
