Time-resolved cyclotron resonance in cuprous oxide

We have demonstrated cyclotron resonance with a temporal resolution of 15 ns by using an electron-spin-resonance cavity. In an undoped direct-gap semiconductor, cuprous oxide, we observe clear low-field shifts of the cyclotron resonance peaks shortly after generation of photoexcited carriers. Based on the plasma shift of the cyclotron resonance, we evaluate the carrier density and quantitatively discuss the interaction between free carriers and excitons. With increasing time delay, the hole resonance asymptotically reaches the constant value corresponding to an effective mass of 0.575 times the free electron mass, providing a definitive answer to the controversy on the effective mass of holes in cuprous oxide.