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Reference : UMR6508-JULVAR-001
Workplace : CAEN
Date of publication : Wednesday, June 03, 2020
Scientific Responsible name : Julien Varignon / Manuel Bibes / Wilfrid Prellier
Type of Contract : PhD Student contract / Thesis offer
Contract Period : 36 months
Start date of the thesis : 1 October 2020
Proportion of work : Full time
Remuneration : 2 135,00 € gross monthly
Description of the thesis topic
Transition metal oxides exhibit a wide range of properties such as magnetism, ferroelectricity or superconductivity, coexisting within in a reduced number of structural families. In particular, ABO3 perovskite oxides have attracted widespread interest from the community due to its great structural flexibility, but also because it is relatively simple to develop as thin films or heterostructures combining several materials exhibiting strong couplings between them and unprecedented properties at interfaces.
Beyond perovskites in which transition metal ions are surrounded by an oxygen cage octahedra within a three dimensional network, several oxides exhibit a two-dimensional organization of cations and anions, and this is the case of the “infinite-layer” compounds of ABO2 chemical formula. These materials are the building blocks of the high critical temperature superconducting cuprates (SrCuO2) [Nature 351, 549 (1991)] once properly doped. However, they remain less studied than the classical ABO3 oxide perovskites.
Very recently, a new phase of the “infinite-layer” family has been identified as a new superconductor [Nature 572, 624 (2019)] : the Sr doped NdNiO2 material. This discovery crowns ten years of research of superconductivity in Ni-based oxides [PRL 100, 016404 (2008)] and paves the way toward the identification of new oxide superconductors.
The proposed thesis subject aims to understand the physics of (Nd, Sr)NiO2 compounds and the origin of the superconducting phase. According to the results obtained, other perovskites, involving materials similar to the rare earth nickelates RNiO3 (R = Lu-La, Y) could be explored in their "infinite layer" phase. The thesis will be organized in two parts. The first part will be theoretical and mainly carried out at the Laboratoire de Cristallographie et Sciences des Matériaux (CRISMAT, W. Prellier, J. Varignon, http://www-crismat.ensicaen.fr). This part will be based on electronic structure first-principles calculations carried out within the framework of the density functional theory (DFT) allowing to identify structural, magnetic and electronic properties of NdNiO2 in bulk and under strontium doping. The second part will be experimental and mainly conducted at Unité Mixte de Physique CNRS/Thales (UMPHy, M. Bibes, http://oxitronics.cnrs.fr). This part will be devoted to the development of “infinite layer” phases in the form of thin layers using pulsed laser deposition, followed by an ex situ annealing in a hydrogen-rich atmosphere by CaH2 decomposition. The samples will be characterized by X-ray diffraction, magnetotransport measurements and X-ray spectroscopy at UMPHy.
The candidate should have a strong background in condensed matter physics and be familiar with numerical simulations (notably on DFT). In addition, some knowledge in the development of thin layers and their structural characterization would be a plus.
The candidate will perform his thesis in joint supervision between the "Laboratoire de Cristallographie et Sciences des Matériaux" (CRISMAT-CNRS UMR 6508, J. Varignon, W. Prellier) in Caen and l"Unité Mixte de Physique CNRS Thales" (UMPhy UMR137, Manuel Bibes) in Palaiseau which are both internationally recognized in the field of oxides. This project is part of a experiment/simulation collaboration that exists since 5 years. The PhD student will benefit from a favourable environment to carry out his missions thanks to access to numerous techniques and tools directly in the labs. The project is supported by the CNRS 80Prime2020.
Constraints and risks
Travels between labs have to be expected.
Please provide CV, Cover Letter with two contacts for recommendation The date of recruitment may be postponed until the end of the confinement period.
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