Description du sujet de thèse

The exploration of magnetism at reduced dimension is, especially at two dimensions (2D), rich in non-intuitive phenomena. Unconventional magnetic orders, non-trivial kinds of disorders and intriguing phase transitions have been predicted or observed. Starting from 2016-2017, new experimental platforms have been discovered to address this physics: cristalline 2D materials that can be isolated in the form of monolayers with thickness of one or few atoms. They can be manipulated in different ways by stacking them with other 2D materials, thereby creating artificial materials, or by subjecting them to mechanical constraints for instance. Besides (dis)ordered magnetic states, these materials host photonic and phononic excitations that can couple to the spin degree of freedom, which further enriches the study of magnetism in the 2D limit.
The PhD thesis project will be a fundamental work meant to explore the properties of some of these remarkable magnetic 2D materials, standing out for their high magnetic ordering temperature or for a coexistence of different types of quantum excitations. The goal is to explore ways to manipulate 2D magnetism in these materials, which will be done by subtly modifying the materials' chemical composition, applying external pressure or using strong magnetic fields. To understand the magnetic properties and their relationship with magnons, phonons and the coupling between these quasi-particles, fine spectroscopy techniques will be employed, especially Raman light scattering in a broad range of conditions, down to low temperatures, up to high pressures (GPa) and in presence of magnetic fields reaching tens of Teslas.

Contexte de travail

The work will be performed within two laboratories located at the same geographical area, the Néel Institute where sample fabrication and advanced magnetic characterisations (imaging, magnetometries) are mastered, and the High Magnetic Field Laboratory, where optical spectroscopy experiments will be done under extreme conditions. The work will be mainly experimental and will benefit from interactions with local experts in materials synthesis and in complementary spectroscopy techniques. The project is part of a larger, national-scale endeavour implying seven laboratories.
The job is linked to the Hybrid team, research team which works on electronic, optical, vibrational and mechanical properties of hybrid systems at the quantum scale, and the coupling between these properties.
The PhD candidate, who should have a strong condensed matter physics background, will be in charge of preparing the samples that will be suited to the different kinds of measurements he/she will next take care of, in certain cases in collaboration with local experts, to characterise the structure, optical and magnetic properties, in presence of strong magnetic fields.
The Institut NEEL is a CNRS laboratory. CNRS is a public, scientific and technological organisation. The core mandate is to identify, carry out ou have carried out, either alone or with partners, all research that advances science or contributes to the country's economic, social, and cultural progress. Internationally recognised for the excellence of its scientific research, the CNRS is a reference in the world of research and development, as well as for the general public.

Le poste se situe dans un secteur relevant de la protection du potentiel scientifique et technique (PPST), et nécessite donc, conformément à la réglementation, que votre arrivée soit autorisée par l'autorité compétente du MESR.

Contraintes et risques

The optical spectroscopy experiments imply the use of lasers and related safety measures. The PhD candidate will receive a training addressing these safety issues. Experiments under intense magnetic fields are also associated with safety issues, and are in particular incompatible with medical devices related to cardiac diseases. Besides, these experiments will be performed in the framework of measurement campaigns (typically 2 to 3 sessions per year, each lasting 1 week) implying overnight working hours.