Description du sujet de thèse

The magnetic and electronic transport properties of some quantum materials challenge the standard model of metals. This physics is based on notions such as the existence of quasiparticles that carry electric charge. What happens when this notion ceases to be valid? How is charge transported when it evolves in a magnetic environment that remains disordered down to the lowest temperatures? And how can this magnetic environment, which never orders even at the lowest temperatures, be described? These questions arise in some parts of the phase diagram of some copper oxides. In these systems, it is suspected that the interaction between itinerant charges and the disordered magnetic environment gives rise to new phenomena such as high-critical-temperature superconductivity or the strange metal phase. These phenomena are at the heart of fundamental questions in modern quantum materials physics.

To study these phenomena and answer the questions raised above, we propose to explore the magnetic and electronic transport properties in certain cuprates using ultrasonic and electrical resistivity measurements. These measurements will be carried out in a cryogenic environment and under very high magnetic fields (up to 86 T) using the facilities available at the LNCMI. The ultrasonic technique allows probing magnetism, particularly its dynamics, heterogeneity, and behaviour under field and temperature changes through magneto-elastic coupling. In parallel with electrical transport measurements, these measurements will directly assess the impact of magnetism on electronic charge transport in these systems.

Contexte de travail

The Laboratoire National des Champs Magnétiques Intenses (LNCMI), located on 2 sites (Toulouse and Grenoble), is a CNRS laboratory (UPR3228) and a Très Grand Instrument de Recherche (TGIR). It is associated with INSA Toulouse, Université Grenoble Alpes (UGA), and Université Paul Sabatier (UPS, Toulouse).
The LNCMI enables researchers to carry out experiments in some of the world's most intense magnetic fields. Continuous fields up to 36 T are available at the Grenoble site.

The student will work in the ultrasound group which is composed of 2 PhD students, and 1 CNRS researcher. The student will have access to all of the group's facilities, including a 20 T superconducting magnet and accompanying cryogenic inserts covering a large temperature range, and state-of-the-art instrumentation. The student will lead experiments in high magnetic field, whether in continuous field up to 36 T in Grenoble, or in pulsed magnetic field up to 90 T in Toulouse.

Contraintes et risques

The LNCMI facilities operate 7 days a week, 20 hours a day. Depending on the schedule, experiments on resistive magnets may occasionally be conducted during off-peak hours and on weekends.
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This thesis project requires a broad range of skills, from sample preparation to instrument development in a cryogenic environment, and understanding magnetism in strongly correlated systems. It is therefore aimed at highly motivated candidates with a strong background in quantum materials physics who are ready to take on ambitious experimental challenges.