Charge correlation and transport properties in one-dimensional arrays of tunnel junctions

Walker, K 2015, Charge correlation and transport properties in one-dimensional arrays of tunnel junctions, Doctor of Philosophy (PhD), Applied Science, RMIT University.

Document type: Thesis
Collection: Theses

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Title Charge correlation and transport properties in one-dimensional arrays of tunnel junctions
Author(s) Walker, K
Year 2015
Abstract In this thesis we present a mathematical model and numerical simulations of one-dimensional arrays of small tunnel junctions to investigate correlated charge transport and other transport properties. Our primary motivation for this research is the recent discrepancies between theoretical models and experimental observations in the literature. Several experimentally observed behaviours can not be explained or predicted by the orthodox theory of junction array physics, which has successfully and fully predicted and described charge transport in single tunnel junctions since the 1980s. These findings highlight the need for a complete theoretical framework for multi-junction systems.

We consider linear and bilinear junction arrays in both the normal and superconducting transport regimes. We primarily focus on the correlated charge transport regime, which we find is optimal in the low current (voltage) limit. We initially simulate clean arrays and then investigate the effect of both the weak and maximal background charge disorder limits on correlated transport and the current-voltage characteristics. Disorder, most important at small bias voltages, impedes charge correlations and shifts threshold voltages. At high voltages we find very little difference across the disorder strengths.

An intriguing behaviour of tunnel junction devices manifests when we apply a small offset voltage across the arrays. This voltage offset enforces different charge patterns within the array and as a result the current exhibits significant periodic modulation as a function of the offset. Through quantitative analysis, the specific charge patterns can be identified. Notwithstanding that the integrity of these patterns is largely compromised in the presence of disorder, the current continues to exhibit substantial periodic offset voltage dependence.

In the superconducting regime we discuss the interplay between the different charge carriers and differences in the conduction and transport properties between the normal and superconducting limits. We simulate unexplained experimental observations by including charge disorder and sub-gap leakage into our model.

This work contributes to the knowledge of these devices and the development of a microscopic junction array model which correctly and completely explains all experimental effects. Furthermore, this thesis demonstrates the rich physics contained within these relatively simple circuits and through several of the behaviours reported above, the possibility for even more new effects to be discovered.
Degree Doctor of Philosophy (PhD)
Institution RMIT University
School, Department or Centre Applied Science
Keyword(s) Electron transport
Correlated charge transport
Single charge devices
Josephson effect
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