Domaine, spécialité : Physique de la matière condensée
Unité d’accueil : LLB / NFMQ
Résumé
L’objectif du stage M2 proposé est d’étudier numériquement la dispersion des excitations magnétiques dans KTb3F10 à l’aide d’un modèle hamiltonien. Les simulations seront ensuite comparées aux données expérimentales existantes (c’est-à-dire les spectres d’excitation magnétique de KTb3F10 obtenus par diffusion inélastique des neutrons).
Sujet détaillé
Saving energy thanks to highly efficient thermoelectric and thermal barrier devices has driven the quest for low thermal conductors. In insulators, heat is carried by phonons, collective vibrations of atoms. Over time, a range of strategies has been suggested to hinder phonon velocities and/or mean free paths: use of weak interatomic bonds, strong anharmonicity, nanoscale designs, complex or disordered unit cells.
Another promising concept to further impair the phonon mean-free path has emerged from experimental observations in a variety of rare-earth compounds. Indeed, there is a suspicion that local low energy electronic excitations, so-called crystal field excitations (CEF), significantly reduce the phonon lifetime by virtue of a resonant coupling with phonons. Strikingly, tuning the CEF by applying a magnetic field for instance allows one to strongly modify the heat conductivity.
CEF excitations, however, are also sensitive to magnetic excitations between rare earths. As a result, these local modes become collective and acquire a delicate dispersion. In this context, the aim of the proposed M2 internship is to study numerically this dispersion using a model Hamiltonian. Simulations will then be compared with existing experimental data, in this case the magnetic excitations spectra of KTb3F10.
Lieu du stage
CEA Saclay, (91) Essonne, France
Conditions de stage
- Durée du stage : 6 mois
- Niveau d’étude requis : Bac+5
- Formation : Master 2
- Poursuite possible en thèse : Oui
- Date limite de candidature : 2 mars 2026
Compétences requises
Langue : Anglais
Méthodes, techniques :
During this internship you will:
- Perform calculations of the excitation spectrum of KTb3F10, using a code developed in the LLB laboratory,
- If times permits, expand the model by introducing a magneto-elastic coupling term and compare it with the inelastic neutron scattering data of KTb3F10 at low temperature and various magnetic fields which are already available.
Liens utiles
- Page Internet du responsable de stage : Sylvain Petit.
- Page internet du laboratoire : LLB/NFMQ