We report the first direct measurement of carrier-carrier scattering rates in a degenerate electron system. Our results on modulation-doped quantum wells, using femtosecond four-wave-mixing (FWM) techniques, demonstrate a strong inhibition of scattering near the Fermi edge, and exhibit other behavior predicted by Landau Fermi liquid theory. Time-resolved (100 fs) FWM measurements clearly show photon echoes, demonstrating the inhomogeneous character of this intrinsic system, as well as prompt signals arising from many-body effects.

• Received 29 January 1992

DOI:https://doi.org/10.1103/PhysRevLett.68.2838