Theory of Charge and Heat Transport Mechanisms in Nanodevices

In this thesis, we pursue mechanisms in the nonequilibrium transport of charge and heat, to elucidate nanodevice operation, and explore fundamental theoretical questions. The thesis is divided into two parts. Part I explores in detail the role of incoherent effects on the charge transport behaviour of molecular junctions. Such effects, induced by molecular vibrations, solvent or other environmental effects, play a crucial role in many physical setups, but are difficult to simulate explicitly. We apply the Landauer-B\"uttiker probe technique, a phenomenological approach that incorporates incoherent effects at a low computational cost, and demonstrate the applicability of the technique by verifying that it captures a number of pertinent physical features, and achieves semi-quantitative agreement with experimental data. Going beyond this, we apply the probe method to a number of proposed physical setups. In stacked vs. alternating GC-rich ds-DNA, we find the even-odd effect in the experimentally observed conductance can be explained via a mixed coherent-incoherent transport mechanism. We find that in general, environmental interactions are destructive to the operation of molecular charge rectifiers, though in certain circumstances a weak rectifying behaviour might arise from many-body environmental effects. In Part II of this thesis we shift our focus to heat transport, and particularly the operation of quantum heat machines. We begin with a study of the role of so-called noise-induced coherences on the operation of a quantum absorption refrigerator. While in the past quantum coherences have usually been found to boost power in such setups, we observe a complete shutdown of the device when coherences survive to the nonequilibrium steady-state. We then extend our analysis, developing a general approach that one can use to more easily discover the role of coherences in quantum heat machines. We conclude with the development of a new numerically exact approach, the iterative full-counting statistics path integral (iFCSPI), which is suitable for simulations of heat transport in nanodevices. The iFCSPI allows the calculation of the cumulants of heat transport, as well as strong-coupling and non-Markovian effects, provided it can be converged.

Department dc:contributor.department

Chemistry

Year dc:date.issued

2019

Author dc:creator

• Kilgour, Michael John Andrew

Advisor dc:contributor.advisor

• Segal, Dvira

• Buttiker probe
• Feynman-Vernon path integral
• Molecular junction
• Nanodevices
• Quantum heat machine
• Quantum thermal transport

Handle dc:identifier.uri

http://hdl.handle.net/1807/97509

OAI identifier oai:identifier

oai:utoronto.scholaris.ca:1807/97509