| Summary: | Cyclotron resonance measurements in the highly polar (α = 0.29) semiconductor InSe are reported in pulsed magnetic fields up to 37 T. For B > 18 T two cyclotron branches are found which are a consequence of the resonant polaron interaction. This is the first time that both branches have been observed simultaneously in 2D, and both are observed over a range of more than 10 T. The splitting is approximately 40% of the optical phonon energy which results in a change in effective mass of a factor of two between the upper and lower branches. A detailed comparison is made with a theory for the cyclotron resonance spectrum. A second, much weaker resonant interaction is found for B ≈ 18 T. This is due to a resonant interaction with homopolar phonons and a theory is constructed for this interaction. At resonance the splitting is a very sensitive function of the interaction strength, allowing accurate determination of the coupling constant g2 = 0.001. © 1992.
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