ULTRAFAST DYNAMICS OF COULOMB CORRELATION-EFFECTS IN NONEQUILIBRIUM FERMI SEAS

By spectrally resolving the transient four-wave mixing (FWM) signal an d the differential transmission signal arising from electron-hole pair s optically excited into the continuum of a GaAs/AlGaAs quantum well s tructure, we directly measure the dynamics of the quantum coherence am ong such interacting carriers. We observe a dynamic blue-shift of the coherent FWM emission spectrum with respect to the excitation laser pu lse. We interpret our results in terms of dynamic Coulomb correlation effects arising in non-equilibrium degenerate electron-hole systems.