Expérimental et théorique
The present subject aims at studying strain-induced exotic electronic phases in correlated electron systems presenting such states as charge density waves (CDW), spin density waves (SDW) and/or superconductivity (SC). Thanks to a unique cryogenic biaxial tensile strain device, compatible with optical, tansport and x-ray diffraction (XRD) measurements, we can study lamellar systems that exhibit various electronic orders under strain. We recently showed that application of mechanical strain can induce exotic phase transitions in lamellar systems, like CDW orientational transition only governed by in-plane lattice parameter symmetry, and with a linear evolution of transition temperatures with strain, reaching 40K at maximum deformation. This evolution of Tc is apparently not at all proportional with the gap, and new studies have to be performed in those systems under strain to understand the very nature of these CDW. In this project, we plan to develop and use new types of measurements under strain: the direct band gap measurement by photoemission spectroscopy under strain, the evolution of electron-phonon coupling by time-resolved optical and XRD techniques, and the study of local strain-induced CDW structure by x-ray microdiffraction. Finally, we plan to extend these techniques to other systems presenting competing exotic electronic phases: CDW/CDW and CDW/SC in transition metal dichalcogenides and CDW/SDW in chromium thin metallic films.