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Danial MAJIDI presents

Heat transport in a single quantum dot device

Wednesday, 15th December 2021 à 14h00 

Seminar room, Building A, Institut Néel : number of person limited to 30

Lien visio : https://univ-grenoble-alpes-fr.zoom.us/j/93808573140?pwd=Tjd1WDBUdEFQZHFZaURncUhrTWdlQT09

ID de réunion : 938 0857 3140
Code : 893814

The thesis presentation and the sildes will be in English.


Abstract :

Quantum dots are an attractive model system for basic studies and applications in thermoelectricity, owing to their tunable electronic transmission and electron-hole asymmetry. In the weak coupling regime, the discreteness of the quantum dot energy spectrum makes electronic transport processes strongly selective in energy. The net heat flow is zero in such a device since electrons tunnel back and forth exactly using the same energy level. Therefore, a weakly coupled quantum dot is in principle a good thermal insulator as heat conductance is zero regardless of the position of the quantum dot level with respect to the energy.

We investigate heat flow in two different quantum dot devices. First, in a metallic single quantum dot junction, fabricated using the electromigration technique,  we experimentally measured heat conductance in the presence of strong co-tunneling effects using a sensitive superconductor-normal metal-superconductor (S-N-S) junctions as a local temperature probe of the leads.  We demonstrate the gate control of the electronic heat flow, in agreement with the numerical calculations.  Electron temperature maps taken in the immediate vicinity of the junction, as a function of the gate and bias voltages applied to the device, reveal clearly defined Coulomb diamond structures.  In addition, we combine charge and heat conductances which demonstrate a violation of the Wiedemann-Franz law in the intermediate coupling regime.

Then, we move to InAs nanowire based-devices, as they have attracted considerable attention due to their remarkable tunability on the coupling of the quantum dot and their stability in time for thermoelectric applications.  We report on simultaneous measurements of heat and charge transport using a sensitive superconductor-insulator-normal metal (S-I-N) electron thermometer integrated inside the device. We demonstrated adjustable and strongly energy-selective heat conduction significantly below the Wiedemann-Franz prediction. Moreover, the observed phenomena in both experiments agree well with the theoretical calculations.


Supervisors : 

Hervé Courtois, Professeur, Université Grenoble Alpes/Institut Néel-CNRS, Directeur de thèse
Jukka Pekola, Professeur, Aalto University School of Science, Co-directeur de thèse
Clemens Winkelmann, Maître de conférences, Grenoble INP/Institut Néel-CNRS, Co-directeur de thèse

Jury’s Members  :

Anne Anthore, Professeur, Université de Paris, Rapporteure
Stefano Roddaro, Professeur, Scuola Normale Superiore-Pisa, Rapporteur
Franck Balestro, Professeur, Université Grenoble Alpes, Examinateur
Silvano de Franceschi, Directeur de recherche, CEA Grenoble, Examinateur
Heiner Linke, Professeur, Faculty of Engineering, Lund University, Examinateur