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PhD Thesis-Exploration of the phase diagram of superconducting cuprates by combined optical spectroscopy and thermal transport measurements. (H/F)

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General information

Reference : UMR7162-NATMER0-008
Workplace : PARIS 13
Date of publication : Tuesday, September 08, 2020
Scientific Responsible name : Alain SACUTO
Type of Contract : PhD Student contract / Thesis offer
Contract Period : 36 months
Start date of the thesis : 2 November 2020
Proportion of work : Full time
Remuneration : 2 135,00 € gross monthly

Description of the thesis topic

The true nature of the electronic orders underlying the phase diagram (temperature-doping) of the superconducting copper oxides (known as cuprates) remains a fundamental unresolved question in quantum materials physics to this day. In order to identify the nature of these orders and, in particular, the pseudogap phase from which the superconductivity of cuprates emerges, we propose in this thesis in joint supervision between our team (Pr. A. Sacuto and Pr. Y. Gallais) of the University of Paris (France) and that of Pr. Taillefer from the University of Sherbrooke (Canada), to carry out joint measurements of Raman optical spectroscopy and thermal transport on model materials that are the Nd-LaSrCuO and Eu-LaSrCuO cuprates. These materials are unique in that their superconducting transition temperature is low (on the order of 10 Kelvin), allowing exploration of the pseudogap phase that forms above Tc at relatively low temperatures (10-100K). This makes it possible to reveal the true signature of this phase which at higher temperatures above 200 K would be blurred by thermal excitations. The tracks that we propose to explore will be the links that the pseudogap phase develops with others phases that can be explicitly identified by thermal measurements and Raman spectroscopy such as the spin liquids, the nematic phase (distortion of the electron gas) or the charge density waves.

Références :
A. Legros, et al. « Universal T-linear resistivity and Planckian limit in overdoped cuprates”, Nature Physics 15, 142 (2019).
B. Michon, et al. “Thermodynamic signatures of quantum criticality in cuprate superconductors” Nature 567, 218 (2019).
B. Loret et al. « Intimate link between charge density wave, pseudogap and superconducting energy scales in cuprates ». Nature physics 15, 771 (2019).
N. Auvray et al. « Nematic fluctuations in the cuprate superconductor Bi2Sr2CaCu2O8+” Nature Comm. 10, 5209 (2019).
G. Grissonnanche et al. “Giant thermal Hall conductivity in the pseudogap phase of cuprate superconductors, Nature 571, 376 (2019).

Work Context

We propose in this thesis a co-supervision between our team (Pr. A. Sacuto and Pr. Y. Gallais) from the University of Paris (France) at the laboratory Matériaux et Phénomènes Quantiques (MPQ) and that of Pr. L. Taillefer of the University of Sherbrooke (Canada), to carry out joint measurements of Raman optical spectroscopy and thermal transport on model materials that are the Nd-LaSrCuO and Eu-LaSrCuO compounds.

At the MPQ laboratory in Paris, student (e) will first learn how to master low temperature electron Raman spectroscopy under uni-axial pressure to reveal the signatures of nematic fluctuations on Nd-LaSrCuO compounds and follow their evolution as a function of charge carrier doping up to the vicinity of the quantum critical point where the pseudogap phase ends. This analysis will help identify the links between pseudogap and nematicity. In a second step, we will analyze the charge density wave signatures by Raman spectroscopy, as a function of the doping but also as a function of pressure in Nd-LaSrCuO and Eu-LaSrCuO in order to identify their connection with the pseudogap phase.
The project on the Sherbrooke side, will consist of electrical and thermal transport measurements to elucidate the nature of the pseudogap phase. The student will work on innovative techniques such as the thermal Hall effect, including its development and use in a dilution refrigerator, and the Seebeck effect, particularly along the c-axis (perpendicular to the CuO2 planes of the cuprates). Recent discoveries by our team show that these two techniques, still very little used in cuprates, are very promising.

Constraints and risks

Thesis in co-supervision: The research work will be shared half at the University of Paris (France) and half at the University of Sherbrooke (Canada).

Additional Information

A good knowledge of the fundamental physics of solid state physics at Master 2 level (quantum physics, statistical physics…), a pronounced taste for experiments with an ability to understand theoretical developments for the analysis and understanding of the results.

Desired experiences in a research laboratory (master's or bachelor's degree)

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