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Reference : UPR2940-ELOBER-044
Workplace : GRENOBLE
Date of publication : Friday, June 4, 2021
Scientific Responsible name : BOURGEOIS Olivier
Type of Contract : PhD Student contract / Thesis offer
Contract Period : 36 months
Start date of the thesis : 1 October 2021
Proportion of work : Full time
Remuneration : 2 135,00 € gross monthly
Description of the thesis topic
• General Scope
Phonons, just like electrons, are known to be quantum particles. In a macroscopic material, this quantum nature of the phonons is hidden by the fact that the typical size of the sample is by far larger than the typical wavelength of the phonons. Just like in optics, in this situation, no spectacular effect of the quantum nature of the phonons can be expected. But if you now reduce the dimensionality of a heat conductor down to the limit of the phonon wavelength, then the quantum nature of the phonons should dominate their behaviour: this is a new field of research in which new concepts are still emerging. In this internship, we will focus on how this confinement changes the phonon behaviour and thus the heat transport in 2D structures (membrane) or 1D (nanowires).
As an example, let us ask what happens when the dimensions of the conductor are comparable with the wavelength of the phonons, how can we describe the transport of phonons in such structures? The answer is quite subtle, and is related to the transmission of the wavefunction of the phonons through the structure. The most direct evidence of such a wave-nature of the heat transport in such small systems would thus lie in the appearance of plateaus each time the width of the conductor equals an integer times the wavelength of the phonons. This evidence for the quantum nature of heat transport at low temperature is still not clearly experimentally given.
• Research topic and facilities available
The topic of this thesis holds on phonon transport experiments at very low temperature. These measurements will be carried out in extreme conditions on suspended membranes and nanowires. The experiments will be based on new sensors with sensitivity of the order of Zepto-Joule (10^-21 Joule), a world record at dilution fridge temperatures (10-50mK). The goal is to access the quantum regime of phonon transport and thus the quantum regime of heat conduction by optimizing the transmission coefficient. We will demonstrate the potential manipulation of heat flow using non-symmetric nanostructures to evidence thermal rectification. We will manipulate the heat in low dimensionality systems (1D and 2D), a route towards exchange or storage of information using phonon as heat carrier.
The successful candidate will be jointly supervised by O. Bourgeois and L. Saminadayar (Néel Institut, CNRS).
Collaboration and networking (HANIBAL ANR Project): Collaborations with both theoreticians and experimentalists: Natalio Mingo (CEA, Grenoble), Jean-François Robillard (Lille), and Robert Whitney (LPMMC, Grenoble).
The Institut NEEL (http://neel.cnrs.fr) is a CNRS laboratory for fundamental research in condensed matter physics, in association with the University of Grenoble-Alpes. About 450 people work there. The laboratory is located in Grenoble, in a very rich international scientific environment, in the heart of the Alps.
Constraints and risks
Handling cryogenic liquids will require strict rules to be followed.
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