Landau-level lifetimes are determined from saturation cyclotron resonance measurements on an InAs/GaSb double heterojunction using a picosecond far-infrared free-electron laser. Strong nonparabolicity of the conduction band truncates the equidistant Landau-level ladder, and saturation is achieved at all wavelengths. The Landau-level lifetimes show minima at Nħ${\mathrm{\omega }}_{\mathit{c}}$=ħ${\mathrm{\omega }}_{\mathrm{LO}}$, a direct observation of the magnetophonon effect. Observed picosecond lifetimes are due to LO-phonon emission which dominates electron-electron scattering at the magnetophonon resonance condition. © 1996 The American Physical Society.

• Received 19 January 1996

DOI:https://doi.org/10.1103/PhysRevB.53.16481