Effects of electron-electron scattering in wide ballistic microcontacts.

We calculate the corrections to the Sharvin conductance of ballistic multimode microcontacts that result from electron-electron scattering in the leads. Using a semiclassical Boltzmann equation, we obtain that these corrections are positive and scale with temperature as T(2)ln(EF/T) for three-dimensional contacts and as T for two-dimensional ones. These results are relevant to recent experiments on two-dimensional electron gas contacts.