Resonant polaron coupling of then=2Landau level in InSb

The effect of polaron coupling on free-electron cyclotron-resonance transitions between the $n=1\mathrm{}$ and $n=2\mathrm{}$ Landau levels has been investigated in InSb. The cyclotron-resonance absorption was measured in a sample at 48 K using a high-resolution, Fourier-transform spectrometer in magnetic fields up to 19 kOe. Resonant electron mass enhancement was observed in the region where the $n=2\mathrm{}$ and $n=0\mathrm{}$ plus one LO phonon Landau levels cross. The polaron correction to the effective mass was calculated using Wigner-Brillouin perturbation theory. Good quantitative agreement between theory and experiment was obtained when $\alpha$ the electron-LO-phonon coupling constant, was set equal to 0.041. This value of $\alpha$ is larger than that predicted for InSb by Fröhlich's theory. Possible reasons for this discrepancy are discussed.