FREQUENCY-DEPENDENCE OF SHOT-NOISE IN A DIFFUSIVE MESOSCOPIC CONDUCTOR

Detailed measurements of the voltage, temperature, and frequency depen dence of the nonequilibrium current fluctuations for a diffusive mesos copic conductor are reported. The data confirm predictions that a meso scopic conductor shorter than the electron-electron inelastic length w ill display shot: noise. Furthermore, the low temperatures (100 mK) an d high frequencies (1-20 GHz) used for the measurements allow tests in the high-frequency regime (i.e., hv much less than eV and kT) of the shot noise, which clearly show the influence of vacuum fluctuations. T he quantum noise causes a high-frequency ''cutoff' in the shot noise, i.e., the noise is independent of bias voltage for frequencies v > eV/ h.