Description du sujet de thèse

In the context of climate change and the search for frugal numerical technologies, there is an urgent need to develop new routes in search for improved thermoelectric materials. This theoretical project aims at opening new ways to improve the thermoelectric efficiency of materials, by exploring the phonon drag effect, which arises from the momentum transfer (or drag) between the out-ofequilibrium phonon and electron populations, and which is responsible for the strong increase in Seebeck and Peltier coefficients of thermoelectric materials at low temperature. The concept we aim to explore is the use of substrate as an external phonon bath to provide additional out-of-equilibrium phonons, in order to enhance phonon drag effect and shift it to higher temperatures in the conducting channel. To this end, we aim to develop a numerical approach which would allow to describe the coupled transport of charge and heat carriers at the interface between a conducting system and a phonon bath, with the specific focus on phonon drag effect. In parallel, phonon drag effect will be studied experimentally by our collaborators.

In this theoretical project, we aim to describe the coupled dynamics of electrons and phonons via an approach based on Density Functional Theory and on the solution of coupled Boltzmann transport equations for electrons and phonons which was recently developed in our group and to extend it by including the effect of interface and substrate [1]. In recent years, computational approaches which couple density functional theory (DFT) - based description of the electron-phonon and phonon-phonon scattering rates with the Boltzmann transport equation has been shown to obtain the electron and thermal transport characteristics of many 3D and 2D semiconductors in excellent agreement with experimental measurements [1,2]. Progress in the DFT-based description of the electron-phonon scattering has also allowed to describe the non-equilibrium relaxation dynamics of hot or photoexcited electrons in several materials, in very good agreement with time-resolved spectroscopy experiments [3,4].

This theoretical and computational PhD Project is part of by ANR DragHunt (funding by the French National Research Agency), a collaboration with experimentalists and with other groups of theoreticians is part of the project.
[1] R. Sen, N. Vast, J. Sjakste, Phys. Rev. B 108, L060301 (2023).
[2] J. Sjakste, M. Markov, R. Sen, G. Fugallo, L. Paulatto, N. Vast, Nano Ex. 5 035018 (2024).
[3] Chen, Sjakste et al, PNAS 117, 21962-21967 (2020).
[4] H. Tanimura, J. Kanasaki, K. Tanimura, J. Sjakste, and N. Vast, Phys. Rev. B 100, 035201 (2019).

Contexte de travail

The Irradiated Solids Laboratory (LSI) conducts fundamental research activities in the fields of physics and physical chemistry of materials. It studies the fundamental properties of the solid state and its interactions with electronic, ionic and photonic irradiation. The "Theory of Materials Science" team conducts research along the following axes:
1) Materials and energy: electronic and thermal transport, and their coupling
2) Design of new materials: stability, defects, surfaces & interfaces

This theoretical and numerical PhD project is part of the ANR DragHunt (funding by the National Research Agency), collaboration with experimenters (ILM, Lyon) and with other teams of theoriticians (C2N and SATIE) is part of the project. The PhD student will have access to the team's HPC resources, at the local ( local cluster) and national (GENCI) levels.

Contraintes et risques

No particular risk. Code development and HPC computing.

Informations complémentaires

Knowledge of solid state physics and quantum mecanics is mandatory, interest in modelization, ability and/or willingness for programming is also mandatory. Previous experience with DFT is a plus.