Microwave photoresistivity of a two-dimensional electron gas and the fractional quantum Hall effect

We describe experimental results obtained from microwave photoresistivity measurements in a low-electron-density modulation-doped GaAs-${\mathrm{Al}}_{\mathrm{x}}$${\mathrm{Ga}}_{1\mathrm{-}\mathrm{x}}$As heterojunction. We believe that such sensitive experiments can provide interesting information on the fractional quantum Hall effect.