Evidence for virtual-phonon exchange in semiconductor heterostructures

Measurements of frictional drag between adjacent electron gases in double quantum wells provide strong evidence for phonon-mediated electron-electron interactions. These interactions, which dominate the contribution from simple Coulomb scattering at layer spacings larger than a few hundred Å, are between 20 and 100 times stronger than expected for sequential emission and absorption of real phonons. The observed range of the interactions, substantially smaller than the acoustic phonon mean free path, points to a novel electron scattering mechanism involving virtual-phonon exchange.