Mesoscopic electronics beyond DC transport
By: by Leonardo Di Carlo
Published: 2008
Language: eng
Number of pages: 158
Description: Since the inception of mesoscopic electronics in the 1980's, direct current (dc) measurements have underpinned experiments in quantum transport. Novel techniques complementing dc transport are becoming paramount to new developments in mesoscopic electronics, particularly as the road is paved toward quantum information processing. This thesis describes seven experiments on GaAs/AlGaAs and graphene nanostructures unified by experimental techniques going beyond traditional dc transport. Firstly, dc current induced by microwave radiation applied to an open chaotic quantum dot is investigated. Asymmetry of mesoscopic fluctuations of induced current in perpendicular magnetic field is established as a tool for separating the quantum photovoltaic effect from classical rectification. A differential charge sensing technique is next developed using integrated quantum point contacts to resolve the spatial distribution of charge inside a double quantum clot. An accurate method for determining interdot tunnel coupling and electron temperature using charge sensing is demonstrated. A two-channel system for detecting current noise in mesoscopic conductors is developed, enabling four experiments where shot noise probes transmission properties not available in dc transport and Johnson noise serves as an electron thermometer. Suppressed shot noise is observed in quantum point contacts at zero parallel magnetic field, associated with the 0.7 structure in conductance. This suppression evolves with increasing field into the shot-noise signature of spin-lifted mode degeneracy. Quantitative agreement is found with a phenomenological model for density-dependent mode splitting.

Shot noise measurements of multi-lead quantum-dot structures in the Coulomb blockade regime distill the mechanisms by which Coulomb interaction and quantum indistinguishability correlate electron flow. Gate-controlled sign reversal of noise cross correlation in two capacitively-coupled dots is observed, and shown to arise from interdot Coulomb interaction. Super-Poissonian auto-correlation and positive cross correlation are measured in a multi-lead dot, and shown consistent with dynamical blockade of multi-level transport. Shot noise measurements in graphene nanostructures reveal a Fano factor independent of carrier type and density, device geometry, and the presence of a p-n junction. This result contrasts with theory for ballistic graphene sheets and junctions, and points to strong influence of disorder on transmission. A final experiment investigating the graphene p-n junction in the quantum Hall regime reminds us the power of dc transport. New conductance plateaus are observed at 1 and 3/2× e 2 / h , consistent with recent theory for equilibration of edge states at the p-n interface.
Notes: "November 2007."

Thesis (Ph.D., Dept. of Physics)--Harvard University, 2008.

Includes bibliographical references.