Conditional statistics of electron transport in interacting nanoscale conductors

Interactions between nanoscale semiconductor structures form the basis for charge detectors in the solid state. Recent experimental advances have demonstrated the on-chip detection of single electron transport through a quantum dot (QD). The discreteness of charge in units of e leads to intrinsic fluctuations in the electrical current, known as shot noise. To measure these single-electron fluctuations a nearby coherent conductor, called a quantum point contact (QPC), interacts with the QD and acts as a detector. An important property of the QPC charge detector is noninvasiveness: the system physically affects the detector, not visa-versa. Here we predict that even for ideal noninvasive detectors such as the QPC, when a particular detector result is observed, the system suffers an informational backaction, radically altering the statistics of transport through the QD as compared to the unconditional shot noise. We develop a theoretical model to make predictions about the joint current probability distributions and conditional transport statistics. The experimental findings reported here demonstrate the reality of informational backaction in nanoscale systems as well as a variety of new effects, such as conditional noise enhancement, which are in essentially perfect agreement with our model calculations. This type of switching telegraph process occurs abundantly in nature, indicating that these results are applicable to a wide variety of systems.Comment: 16 pages, 3 figures, to appear in Nature Physic

Porous Silicon and Thermoelectrics

The motivation for, and performance of, silicon nanostructures including porous silicon in thermoelectrics is reviewed. A high thermoelectric figure of merit ZT ~1 has been achieved with a single silicon nanowire and ZT ~0.5 for a porous nanowire array. Very high Seebeck coefficients (3.2 mVK−1) have been achieved in compressed nanoparticles. Data is also presented relevant to two key factors limiting performance in bulk powders. The original size of silicon particles has a significant effect on the thermal conductivities of densified pellets. The intrinsic low electric conductivity can be improved by doping either nanocrystals or surface conductive ligands