Transport Studies in Mesoscopic Quantum Dot Arrays

<strong>Seminar of the School of Physical Sciences -----------------------------------------------------------</strong> Title: <strong>Transport Studies in Mesoscopic Quantum Dot Arrays</strong> Speaker:<strong> Nirat Ray</strong> (Massachusetts Institute of Technology, Cambridge) Date: <strong>February 19, 2015</strong> <strong>Abstract: </strong>The prospect of designing novel materials with tailored electrical, optical, and magnetic properties has intrigued scientists and engineers for years. Building blocks for such "artificial solids" have emerged from recent advances in nanomaterial synthesis, lithography, semiconductors and emerging understanding of their size-dependent properties. Quantum dots (QDs) resulting from quantum confinement in all three spatial dimensions, are often thought of as artificial atoms with discrete charge and energy states. If one were to create a lattice of these artificial atom with sufficiently low disorder it would be possible to create an artificial solid with tunable properties. Broadly speaking, based on the fabrication technique, QDs can be classified into three families, epitaxial, lithographic and colloidal. In this talk, I will present our experimental results on transport measurements on mesoscopic PbS colloidal quantum dot and lithographic GaAs assemblies. We use a novel nanopatterning technique to create colloidal quantum dot arrays with few current paths, and present our findings on the conduction mechanism. We find large noise in the current through such nanopatterned arrays, consistent with conductance fluctuations, and these appear to be universal features of colloidal quantum dot arrays. For GaAs based lithographic arrays, we observe a striking transition from a high resistance (low current) state to low resistance (high current) as a function of increasing source drain bias. This transition occurs over a large range in gate voltage, and temperature, and could be an indication of collective phenomena occurring within these artificial quantum dot lattices.