Saturation spectroscopy and electronic-state lifetimes in a magnetic field in ${\mathrm{I}\mathrm{n}\mathrm{A}\mathrm{s}/\mathrm{A}\mathrm{l}}_x{\mathrm{Ga}}_{1-x}\mathrm{Sb}$ single quantum wells

Saturation spectroscopy of electronic states in ${\mathrm{I}\mathrm{n}\mathrm{A}\mathrm{s}/\mathrm{A}\mathrm{l}}_x{\mathrm{Ga}}_{1-x}\mathrm{Sb}$ single-quantum-well structures has been carried out with the UCSB free-electron laser. An effective Landau-level lifetime is extracted from the cyclotron-resonance (CR) saturation results on a semiconducting sample $\mathrm{}(x=0.5\mathrm{})\mathrm{}$ with the help of an n-level rate equation model. The effective lifetime shows strong oscillations (greater than an order of magnitude) with laser frequency with minima shifted to higher frequencies than given by the simple parabolic magnetophonon resonance condition due to large nonparabolicity in the InAs conduction band. Similar saturation studies of two lines (the X line and CR) in a “semimetallic” sample $\mathrm{}(x=0.1\mathrm{})\mathrm{}$ show markedly different effective lifetimes, demonstrating that the two lines are of different origin.