We demonstrate that a diffusive narrow wire of a length much longer than the elastic scattering length and the phase-coherence length, but of the order of the energy relaxation length, exhibits shot noise with an intensity lower than the full shot-noise level. At 4.2 K, the reduction factor is shown to vary between 0.2 and 0.45, depending on the width of the wire. The reduction is consistent with recent theoretical predictions.
The kinetics of electron transport in quantum point contacts has been studied by means of low-frequency noise spectroscopy. The temperature and frequency (Lorentzian or l / f ) dependences of the noise intensity are found to be device specific, in contrast to the conductance dependence, which universally exhibits a strong quantum size effect at low temperatures. The origin of the Lorentzian noise spectrum is electron trapping and release at a single trap close to the point contact, and is connected to random resistance switching in the time domain, The l / f noise in other point contacts is attributed to a collection of traps in the vicinity of the point contact. A comprehensive model is presented which accounts for the conductance and temperature dependences of the noise in quantum point contacts.
We review the status of the understanding of single-electron transport (SET) devices with respect to their applicability in metrology. Their envisioned role as the basis of a high-precision electrical standard is outlined and is discussed in the context of other standards. The operation principles of single electron transistors, turnstiles and pumps are explained and the fundamental limits of these devices are discussed in detail. We describe the various physical mechanisms that influence the device uncertainty and review the analytical and numerical methods needed to calculate the intrinsic uncertainty and to optimise the fabrication and operation parameters. Recent experimental results are evaluated and compared with theoretical predictions. Although there are discrepancies between theory and experiments, the intrinsic uncertainty is already small enough to start preparing for the first SET-based metrological applications.
DFM-98-R27Towards single-electron metrology 2
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