Frequency Dependence of Shot Noise in a Diffusive Mesoscopic Conductor

Abstract

Detailed measurements of the voltage, temperature, and frequency dependence of the nonequilibrium current fluctuations for a diffusive mesoscopic conductor are reported. The data confirm predictions that a mesoscopic conductor shorter than the electron-electron inelastic length will display shot noise. Furthermore, the low temperatures (100 mK) and high frequencies (1--20 GHz) used for the measurements allow tests in the high-frequency regime (i.e., $h\ensuremath{\nu}\ensuremath{\gg}\mathrm{eV}$ and $\mathrm{kT}$) of the shot noise, which clearly show the influence of vacuum fluctuations. The quantum noise causes a high-frequency ``cutoff'' in the shot noise, i.e., the noise is independent of bias voltage for frequencies $\ensuremath{\nu}>\mathrm{eV}/h$.