Energy distribution function of quasiparticles in mesoscopic wires

We have measured with a tunnel probe the energy distribution function of Landau quasiparticles in metallic diffusive wires connected to two reservoir electrodes, with an applied bias voltage. The distribution function in the middle of a 1.5-mu m-long wire resembles the half sum of the Fermi distributions of the reservoirs. The distribution functions in 5-mu m-long wires are more rounded, due to interactions between quasiparticles during the longer diffusion time across the wire. From the scaling of the data with the bias voltage, we find that the scattering rate between two quasiparticles varies as epsilon(-2), where epsilon is the energy transferred.