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PhD subjects

Dernière mise à jour : 18-01-2018

2 sujets IRAMIS

«««

• Mesoscopic physics

 

Out-of-equilibrium thermoelectric transport in quantum conductors

SL-DRF-18-0459

Research field : Mesoscopic physics
Location :

Service de Physique de l'Etat Condensé (SPEC)

Groupe Mésocopie Modélisation et Thermoélectricité (GMT)

Saclay

Contact :

Geneviève FLEURY

Alexander SMOGUNOV

Starting date : 01-10-2017

Contact :

Geneviève FLEURY

CEA - DRF/IRAMIS/SPEC/GMT

0169087347

Thesis supervisor :

Alexander SMOGUNOV

CEA - DRF/IRAMIS/SPEC/GMT

0169083032

Personal web page : http://iramis.cea.fr/spec/Pisp/genevieve.fleury/

Laboratory link : http://iramis.cea.fr/spec/GMT/

This subject is now receiving CEA funding as a "flagship" topic. The selection of the candidatures received will be made at the beginning of spring 2018.



Seebeck and Peltier thermoelectric effects provide an eco-friendly way of converting heat into electricity and vice-versa. Thus it is possible with the Seebeck effect to harvest waste heat for producing electricity. Conversely, the Peltier effect enables local cooling of a device by investing electrical power. For a long time, thermoelectric conversion has been limited by a poor efficiency and therefore, practical applications have till date remained rare. Interest in the field has been recently rekindled by the discovery of new promising materials, by progress in nanostructuration, and by the growing societal concern about energy issues.



The purpose of this theoretical PhD thesis is to study analytically and numerically thermoelectric conversion in low-dimensional mesoscopic systems. We will consider the regime far from equilibrium where important thermoelectric effects are expected. In particular, we will investigate systems under dynamic time-dependent forcing. From a methodological standpoint, we will use the numerical tools and the analytical formalism developed at CEA-Grenoble (X. Waintal's team) for the study of (out-of-equilibrium) time-resolved quantum transport (see https://kwant-project.org/). We will adapt it to the case of thermoelectric transport and apply it to various systems (quantum dots, quantum point contacts, nanowires…).

Quantum heat transport in graphene Van der Waals heterostructures

SL-DRF-18-0412

Research field : Mesoscopic physics
Location :

Service de Physique de l'Etat Condensé (SPEC)

Groupe Nano-Electronique (GNE)

Saclay

Contact :

François PARMENTIER

Patrice ROCHE

Starting date : 01-10-2018

Contact :

François PARMENTIER

CEA - DRF/IRAMIS/SPEC/GNE

+33169087311

Thesis supervisor :

Patrice ROCHE

CEA - DRF/IRAMIS/SPEC/GNE

0169087216

Laboratory link : http://nanoelectronics.wikidot.com/research

The goal of this project is to explore quantum transport of heat in new states of matter arising in ultra-clean graphene in high magnetic fields, using ultra-sensitive electronic noise measurements.



The ability to obtain ultra-clean graphene (a two-dimensional crystal made of Carbon atoms in a honeycomb lattice) samples has recently allowed the observation of new phases of condensed matter in graphene under high magnetic fields. In particular, new states of the quantum Hall effect were observed at low charge carrier density [1], where interactions and electronic correlations can either make graphene completely electrically insulating, or give rise to the quantum spin Hall effect. In the latter, the bulk of the two-dimensional crystal is insulating, while electronic current is only carried along the edges of the crystal, with opposite spins propagating in opposite directions. The exact nature of those various states is still not fully understood, as one cannot probe the properties of the insulating regions by usual electron transport measurements.



We propose a new approach to probe those phases, based on the measurement of quantum heat flow carried by chargeless excitations such as spin waves, at very low temperature. Our method will consist in connecting the graphene crystal to small metallic electrodes which will be used as heat reservoirs. The temperature of each reservoir will be inferred by ultra-sensitive noise measurements [2], allowing us to extract the heat flow.



The first step of this project will consist in fabricating the samples made of graphene encapsulated in hexagonal boron nitride [3]. This technique, which we have recently developed in our lab, allows to obtain large-area, ultra-clean graphene flakes. In parallel, an experimental platform for low-temperature, high magnetic field, ultra-high sensitivity noise measurements will be set up.



[1] Young et al., Nature 505, 528-532 (2014).

[2] Jezouin, Parmentier et al., Science 342, 601 (2013).

[3] Wang et al., Science 342, 614 (2013).

 

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