Charge and Heat Transport in Low dimensional Quantum Systems

Abstract

Transport of electrons through low-dimensional quantum conductors like nano-junctions has been actively pursued research area for the last few decades. Experimental studies on nano-junctions are nowadays routinely carried out around the globe thanks to the invention of nanoscale analysis and manipulation techniques like the scanning tunneling microscope and the atomic force microscope. The research on charge and heat transport in nano-junctions is not only motivated by the miniaturization of electronic devices relevant for applications, but also by the intriguing quantum mechanical transport phenomena which differ from that in macroscopic conductors. Motivated by the feasibility of experimentally testing the theoretical predictions of various aspects of transport through quantum junctions, the theoretical work on charge and heat transport through nano-junctions presented in this thesis is carried out using quantum master equation and non-equilibrium Green functions approaches. In chapter 1, experimental works that have motivated the theoretical work presented in this thesis are briefly discussed, followed by a summary of key theoretical techniques which are used to rationalize these experiments. A survey of important works on fluctuations of charge and heat transport in quantum systems and fluctuation theorems satisfied by these fluctuations is also presented in this chapter. In chapter 2, the effect of system-reservoir coupling on charge currents flowing through nano- junctions is studied using non-equilibrium Green functions method applied to two double-quantum dot circuits. It is found that the charge currents do not always increase with the increasing system- reservoir coupling strength. Further, this behavior depends on the way nanosystem is coupled to the reservoirs. For the case when two quantum dots are serially coupled, that is, when the two dots are coupled to two different reservoirs, the current exhibits a non-monotonic behavior and diminishes for large coupling strengths. While for the case where...