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Energetics in metallic-island and quantum-dot based single-electron devices

Abstract : At this age of technologically advanced world, the electronic devices are getting more and more densely packed with micro-electronic elements of nano-scale dimension. As a result the heat dissipation produced in these microelectronic-circuits is also increasing immensely, causing a huge amount of energy loss without any use. The thermoelectric effects come into play here as one can use this wasted heat to produce some useful work with the help of thermoelectric conversion. In order to achieve such a heat engine with a reasonably high efficiency, one needs to understand its thermal behavior at the basic level. Therefore, the study of thermal transport and thermoelectric effect in nano-structures has significant importance both from scientific and application point of view.In this thesis we present the experimental studies of thermal and thermoelectric transport in different kinds of single-electron devices, where the electronic flow can be controlled at the single electron level.First, we demonstrate the measurement of gate-controlled heat transport in a Single-Electron Transistor (SET), acting as a heat switch between two heat reservoirs. The measurement of temperature of the leads of the SET allows us to determine its thermal conductance with the help of a steady state heat-balance among all possible paths of heat flow. The comparison of thermal conductance of the SET with its electrical conductance indicates a strong violation of the Wiedemann-Franz (WF) law away from the charge degeneracy.Second, we extend the study of thermal transport in single-electron devices to the quantum limit, where in addition to the Coulomb interactions the quantum effects are also need to be taken into account, and therefore the individual discrete electronic levels take part in the transport process. We discuss the heat-balance between two heat reservoirs, coupled through a single Quantum-Dot (QD) level, and the dissipation of the tunneling electrons on the leads. This produces Coulomb-diamond shapes in the electronic-temperature map of the `source' lead, as a function of bias and gate voltage. Third, we present the measurement of thermoelectric transport in a single QD junction, starting from the weak coupling regime to the strong coupling-Kondo regime. The experiments introduces a new way of measuring thermovoltage realizing a close to perfect open-circuit condition. The thermopower in a weakly coupled QD shows an expected "e" periodic behavior with the gate-induced charge, while it shows a distinct "2e" periodic feature in the presence of Kondo spin-correlation. The temperature dependence study of the Kondo-correlated thermopower reveals the fact that the Kondo-resonance is not always pinned to the Fermi level of the leads but it can be slightly off, in agreement with the theoretical predictions. This study opens the door for accessing a single QD junction to operate it as a QD-heat engine, where the thermodynamic properties of the device are governed by the laws of textit{quantum thermodynamics}.
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Submitted on : Friday, March 1, 2019 - 8:33:08 AM
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Bivas Dutta. Energetics in metallic-island and quantum-dot based single-electron devices. Condensed Matter [cond-mat]. Université Grenoble Alpes, 2018. English. ⟨NNT : 2018GREAY055⟩. ⟨tel-02024282v2⟩



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