Dephasing times in a classical two-dimensional electron gas

We present the first systematic study of the dephasing times for a classical two-dimensional electron gas. Weak localization occurs due to quasi-elastic scattering of electrons bound above a liquid helium surface from quasi-static helium vapor atoms. There are three dephasing mechanisms for this system. These mechanisms are electron-electron interactions and the motion of the helium vapor atoms parallel and perpendicular to the two-dimensional electron layer. Dephasing by the motion of atoms perpendicular to the surface is studied by varying the holding field to change the characteristic width of the two-dimensional electron layer. Both of the dephasing times due to parallel and perpendicular motions are functions of the elastic scattering time tau0 of the electrons. We were able to measure the dephasing times over a wide range of tau0, which is inversely proportional to the helium vapor-atom density. The dephasing time due to electron-electron interactions is found to be dependent on the two-dimensional electron density.