Cyclotron-resonance oscillations in a two-dimensional electron-hole system

Pronounced oscillations have been observed in linewidth, amplitude, and mass of electron cyclotron resonance in InAs/${\mathrm{Al}}_{\mathit{x}}$ ${\mathrm{Ga}}_{1\mathrm{-}\mathit{x}}$Sb quantum wells when holes coexist with electrons. The strength of the oscillations increases sensitively with electron-hole pair density; the oscillations are absent for semiconducting samples (x≳0.3) in which there are no holes. Results are interpreted in terms of a filling-factor-dependent electron-hole interaction.