From excitons waves to THz-phonons: 2Ds materials nano-optics via synchrotron infrared nanospectroscopy

Abstract

Superconductivity in atomically thin topological insulators, ferromagnetism in van der Waals crystals and magical angles regulating high TC superconductivity in graphene twisted bilayers are extraordinary discoveries that have, surprisingly, occurred just in the last 2 years. This type of advance has been routine in the last decade as a consequence of the impact of the discovery of graphene and of other two-dimensional materials (2Ds). In the context of new 2D materials and the new physics revealed by these quantum platforms, a variety of phenomena occur in the energy range of a few meV (frequencies of some terahertz), are spatially confined in nanometric volumes and have temporal dynamics from femto to picoseconds. In this parameters space, there are no available experiments capable of accessing these new phenomena in their fullness. This research project is aimed at the development of a pioneering instrumentation that will combine broadband synchrotron radiation in the infrared (IR) and THz (IMBUIA beamline of Sirius) with narrowband lasers in the range of the far-IR to visible in the experiment of scattering Scanning Near-field Optical Microscopy (s-SNOM), an ultramicroscopy modality beyond the classical diffraction limit of light. The project also aims to provide access to ultrafast phenomena in these 2Ds through pump and probe experiments by combining the few picoseconds wide pulse from Sirius with ultrashort pulses from narrow band lasers tunable from the visible to the THz ranges. Given the low energy of these phenomena, the experimental development also predicts the implementation of a cryogenic stage up to 20 K. The experimental development has the scientific target of studying local dielectric properties of 2D materials in general, with special attention to open questions involving nanophotonic properties of systems based on graphene/hexagonal Boron Nitride and Phonon-polaritons waves in Transition Metals Dichalcogenides. The project will be a milestone for the establishment of a new research group on the theme of nano-optics of 2D materials using synchrotron s-SNOM and will put Brazil at the forefront of this instrumental modality, since there are no records of s-SNOM experiments operating in mode of spectroscopy in the range of THz with spatial resolution of a few nanometers. The execution of the proposal will involve the training of 3 students and will count on the performance of 2 associated researchers, 1 post-doc and 2 physical engineers of CNPEM. The project also foresees an expressive improvement in the sensitivity of the s-SNOM technique, which will enable its application in several other disciplines, serving the LNLS multiuser community promptly. During the transition period for the new Sirius accelerator (2019 to 2021), the laser sources requested in this proposal will partially meet the demands of this LNLS user program. (AU)