Electron-electron scattering and the transport properties of two-dimensional ballistic contacts

Recent results on the effect of electron-electron collisions on the electric properties of contacts to a twodimensional electron gas with a direct conductivity in the absence of scattering by impurities and boundaries have been reviewed. A correction to the conductance of such contacts owing to the electron-electron scattering can be either positive or negative depending on the contact geometry. The magnitude of this correction strongly depends on the magnetic field.