Asymmetric conductance and coherence effects in mesoscopic Si metal-oxide-semiconductor field-effect transistors

The conductance of Si metal-oxide-semiconductor field-effect transistors (MOSFET's) of submicrometer dimensions has been studied as a function of source-drain voltage, gate voltage, and magnetic field. At liquid-helium temperatures, and for very small source-drain voltage VSD, the conductance was observed to exhibit so-called ``universal'' fluctuations. As VSD was increased, the conductance became increasingly nonlinear and asymmetric, with magnetic-field-dependent structure. This behavior was found to persist even when eV_SDkBT. The data demonstrate that these reproducible deviations from Ohm's law are caused by quantum-interference effects, as has been theoretically predicted for disordered metallic samples.