Abstract
Cyclotron‐resonance lines in n‐type GaAs at 4.2°K are observed to be anomalously narrow when measured at λ = 220 μm. Analysis of the resonance line yields an effective mass ratio of 0.068m0 and an electron‐impurity scattering time of 3.9×10−12 sec compared to a dc scattering time of 4×10−15 sec.