Thermal Conductance of a Single-Electron Transistor

Orateur : Hervé COURTOIS (Institut Néel/UGA)

The flow of heat at the microscopic level is a fundamentally important issue, in particular if it can be converted into free energy via thermoelectric effects . The ability of most conductors to sustain heat flow is linked to the electrical conductance via the Wiedemann-Franz law. While the understanding of quantum charge transport in nano-electronic devices has reached a great level of maturity, heat transport experiments are lagging far behind, for two essential reasons : (i) unlike charge, heat is not conserved and (ii) there is no simple thermal equivalent to the ammeter. Heat transport can nevertheless give insight to phenomena that charge transport is blind to. As device dimensions are reduced, electron interactions gain capital importance, leading to Coulomb blockade in mesoscopic devices in which a small island is connected by tunnel junctions. A metallic island connected to a source and a drain through tunnel junctions exceeding the Klitzing resistance and under the influence of a gate electric field constitutes a Single-Electron Transistor (SET). In the regime where charge transport is governed by unscreened Coulomb interactions, the question of the associated heat flow has been addressed by several theoretical studies. The Wiedemann-Franz law is expected to hold in an SET only at the charge degeneracy points in the limit of small transparency, where the effective transport channel is free from interactions, and is violated otherwise. We will report on the measurements of both the heat and charge conduction through a metallic SET, with both quantities displaying a marked gate modulation. A strong deviation from the Wiedemann-Franz law is observed when the transport through the SET is driven by the Coulomb blockade, as the electrons flowing through the device are then filtered based on their energy.

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