EVIDENCE FOR VIRTUAL-PHONON EXCHANGE IN SEMICONDUCTOR HETEROSTRUCTURES

Measurements of frictional drag between adjacent electron gases in dou ble quantum wells provide strong evidence for phonon-mediated electron -electron interactions. These interactions, which dominate the contrib ution from simple Coulomb scattering at layer spacings larger than a f ew hundred angstrom, are between 20 and 100 times stronger than expect ed for sequential emission and absorption of real phonons. The observe d range of the interactions, substantially smaller than the acoustic p honon mean free path, points to an electron scattering mechanism invol ving virtual-phonon exchange.