A New Spin on High-Temperature Superconductor Problem – neptun

Our strategy will consist in the use of extremely intense magnetic fields to suppress superconductivity together with complementary techniques to probe the macroscopic (transport), microscopic (NMR) and symmetry-related (sound velocity, Raman spectroscopy) properties of these phases.
Our strategy is to attack the pseudogap problem from different fronts: we wish to characterize the pseudogap itself, the associated electronic orders and the possible signatures of quantum criticality. Resolving the Fermi surface of the strange pseudogap metal will represent an important step towards understanding its nature.

The novelty of the project is twofold. First, the addressed questions are, to a large part, new questions raised by recent developments. Second, we ambition to adapt and expand our complementary expertise in transport measurements, ultrasound, NMR and electronic Raman spectroscopy, to novel methods such as focused ion beam (FIB) sample preparation, record-breaking magnetic fields (including quantum oscillations up to 200 T and NMR in pulsed fields) as well as uni-axial-strain control. Therefore, our project represents a truly innovative approach to the high-Tc problem. While being experiment-driven, the project will be carried out in close collaboration with theoretical experts.

The aim of this project is to produce a substantial progress in a 30-year old problem that remains at the forefront of hot topics in condensed-matter physics. Our research project is fundamental in nature so the expected impact, and our motivation, is not technological but rather pushing the frontiers of knowledge. Basic understanding of high temperature superconductivity may lead to significant improvement in the material properties and their application potential. The performances anticipated from our project are very ambitious as they should shed light on the mechanism of high temperature superconductivity. We thus anticipate that our results will have a large international impact, which implies on our side a major effort on the dissemination of knowledge.

The dissemination of scientific and technical results can be viewed from several angles:
- Publications of original articles in high-impact peer-review journals (in open access form whenever possible and with posting on the arXiv and HAL platforms).
- Communications in national and international conferences/workshop such as Materials and Mechanism of superconductivity (M2S), APS March meeting, Gordon Conference, SCES, Low Temperature Physics, Aspen conference...
- Press releases will be published as we already did in the past in cooperation with the communication service of the CNRS.
- Popularization articles in broad audience scientific journals (Images de la Recherche du CNRS, Journal du CNRS, Physics Today, etc.) as we already did in the past.
- Publication of highlights in annual reports.
- Electronic publications via the Internet (e.g., articles or videos through institution websites)
- Training of PhD students and post-doctoral students

The enduring question of what causes high temperature superconductivity in copper oxides has remained one of the most profound problems in condensed matter physics. Recent progress in the field has revealed that the pseudogap state, which is considered as the crux of the problem, hosts several quantum phases. In these phases, certain components of the electronic system become ordered, that is, they spontaneously break particular (translational, point-group and time-reversal) symmetries.

The goal of our project is to understand the relationship between these “electronic orders” and the pseudogap phenomenon. This includes fundamental questions such as the microscopic nature and the origin of the various electronic orders, their exact dependence on carrier concentration and their possible relationship with each other’s as well as the question as to whether one (or several) of these orders is responsible for the spectroscopic pseudogap and the question of what fundamental symmetry (symmetries) the pseudogap state breaks (if any), in a general and universal manner.

To achieve this goal, we shall use innovative experimental methods such as focused ion beam sample preparation, record-breaking magnetic fields as well as uniaxial-strain control. These new methods will complement a general strategy of quenching superconductivity with intense magnetic fields in order to reveal the underlying “normal” state at the lowest temperatures, through an arsenal of complementary techniques: transport, sound velocity, NMR and electronic Raman spectroscopy.

Our project aims at bringing together recognized experts of these techniques in Toulouse (LNCMI-CNRS), Grenoble (LNCMI-CNRS) and Paris (MPQ Paris-Diderot), in order to perform coordinated measurements on single crystals of the highest quality in various cuprate families (Y, La, Bi or Hg-based). We believe that this synergistic and innovative effort will significantly move the field forward. Understanding the mechanism of superconductivity in copper-oxides would not only push the frontiers of knowledge in condensed-matter physics. It would also facilitate the discovery of new superconductors with higher transition temperatures, which would inevitably widen the range of technological applications of superconductivity. Furthermore, the progress in cutting-edge instrumentation and the know-how acquired during the project will benefit the entire community of users of high-field facilities.

Dissemination of knowledge is an essential part of this project. The project will provide first-class playground for the training of PhD students and post-doctoral fellows. They will be trained in cutting-edge experimental techniques, they will be involved in all aspect of research at an internationally-competitive level, including the use of high-field facilities and they will be advised by leaders in their field. Young scientist will also be encouraged to gain useful experience at (both national and international) conferences and summer schools. They will also be associated with regular outreach activities in the different labs in order to enthuse the next generation of scientists. The transfer of knowledge from the host institutions to these young researchers will enable them to play a pivotal role in the scientific community and in large-scale facilities.