Transport micro-onde sous champ magnétique dans les matériaux quantiques
Bibliographic record
Abstract
Superconductors enable lossless electrical transport and are materials of interest for future technologies such as energy transport, magnetic levitation, quantum information and many other innovations in medicine. Superconductivity was discovered by Kamerlingh Onnes in 1911, and the BCS theory that describes it was formulated in 1957. Nevertheless, a class of so-called unconventional superconductors, such as the high-temperature superconductors (cuprates) discovered by Bednorz and Müller in 1986, remain partially misunderstood. The phase diagram of these compounds is complex and poorly understood. This thesis addresses this issue by studying two phenomena in the cuprate phase diagram: 1) the pseudo-gap ground state and 2) Planckian dissipation.The pseudo-gap is a mysterious phase that could reveal crucial information about the origin of high-temperature superconductivity. Superconductivity is very robust at the point where this phase disappears. To probe its fundamental state in the cleanest cuprates, we need to subject the sample to a magnetic field of around 150 T at low temperature to suppress superconductivity. This would enable us to measure quantum oscillations or the Shubnikov - de Haas effect, which is a consequence of the transition from the Landau levels to the Fermi energy level as the magnetic field increases. The frequency of quantum oscillations is directly proportional to the area of the Fermi surface of the material under study. Determining this Fermi surface will therefore provide a better understanding of the nature of the fundamental state of the pseudogap. Setting up a Megagauss experiment operating at high magnetic fields (in excess of 150 T) was at the heart of my work at LNCMI-Toulouse. An RF measurement circuit was designed and improved during this thesis. Measurements on known materials such as InAs, InSb and WTe2 were carried out to show that the experimental device is reliable and operational for use on cuprates.Another part of this thesis focuses on Planckian dissipation, a phenomenon commonly observed around a critical quantum point. Unlike usual metals whose resistance varies with T², some quantum materials show a linear temperature dependence. This linear variation is thought to be due to the maximum diffusion rate permitted by quantum physics. By measuring conductivity as a function of frequency and using the extended Drude model, it is possible to extract a relaxation time directly, enabling Planckian dissipation to be tested. A microwave transport measurement experiment (F=40 GHz) under a magnetic field (B=7 T) and at very low temperature (T=0.3 K) has been developed at the University of Sherbrooke to study this phenomenon. Measurements on the heavy fermion CeCoIn5 were carried out and enabled us to extract a relaxation time close to the quantum critical point.
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.001 |
| Meta-epidemiology (narrow) | 0.001 | 0.001 |
| Meta-epidemiology (broad) | 0.001 | 0.000 |
| Bibliometrics | 0.001 | 0.000 |
| Science and technology studies | 0.002 | 0.002 |
| Scholarly communication | 0.003 | 0.002 |
| Open science | 0.000 | 0.001 |
| Research integrity | 0.001 | 0.002 |
| Insufficient payload (model declined to judge) | 0.009 | 0.002 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".