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(E(F)/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.