| dc.description.abstract | Thermodynamic probes, such as heat capacity measurements, are a well-established tool for characterising phase properties of complex bulk materials, such as spin-ice, 2D electron gas or baro- or magnetocaloric materials. However, the standard techniques cannot be applied to microscopic systems, as the decreasing system size leads to the requirement for increasingly precise heat flow measurements – an experimentally difficult task. A promising recent alternative is based on electrical measurements, allowing to find the entropy of a nanodevice through charge state or charge transport measurements. These are the main focus of this thesis. I begin by formulating a universal thermodynamic framework that describes all previous electric thermodynamic measurements in nanodevices, discussing all quantities involved, and deriving an analogue to a Maxwell relation which is applicable to a system with significant energy and particle number fluctuations. I then propose a new entropy measurement method based on thermoelectric susceptibility, which has several advantages other previous ones, such as the reduced number of fitting parameters and the lack of sensitivity to charge traps. Applied to a single-molecule nanodevice it can reveal the electronic level structure of the freeradical molecule and the presence of a singlet-triplet transition in it. Next, I present a completely new approach to entropy measurements based on the non-equilibrium fluctuation relation, which makes it highly system-independent and applicable in highly out-of-equilibrium states. This is supported with experimental data for a molecule with two spacial localisation sites. After that, I discuss the limitations of the presented methods due to various effects, including strong coupling (finite lifetime of electron in the system), large energy level splitting, electron-vibrational coupling and the presence spin-selection rules. I conclude with a discussion of future directions of study, both in systems the methods can be applied to, and their potential for significantly simplifying experiments in quantum thermodynamics, as being able tomeasure thermodynamic quantities of electric nanoscale systems will allow for them to be used in fundamental research. | en_US |
