Atomic-Scale Imaging of Exciton and Phonon Dynamics in Quantum Materials

Accessing the atomic scale structural and electronic properties is crucial to understand fundamental correlated properties in quantum materials. In recent times, analytical electron microscopy techniques such as scanning transmission electron microscopy (STEM)-electron energy loss spectroscopy (EELS) under cryogenic conditions have been applied to image local bosonic states such as excitons and phonons. My talk will be focused on probing these bosonic states at low temperatures. I would start my talk with moiré two-dimensional transition metal dichalcogenides which have correlated electronic states resulting from atomically varying strains associated with the stacking configuration. I will talk about the recent progress that we have made in cryogenic imaging excitons in moiré two-dimensional transition metal dichalcogenide heterostructures at the atomic scale from barely detecting the moiré exciton signal in EELS [1] to imaging these excitonic states at the atomic scale [2] to recognizing the fine structure of the moiré excitons [3]. I would also elaborate on the future cryogenic experiments that could be performed on these systems. In the second part, I will take the example of a thin film PbTiO₃ layer grown on DyScO₃substrate [4] and explain how the phonon properties vary near the domain walls. I hope to end my talk by provinding insights about future for cryogenic electron spectroscopy to be successful in accessing fundamental structural and electronic states in quantum materials with some of the pathways that our group is adopting to solve this problem.<br/><br/>[1] S. Susarla, L. M. Sassi, A. Zobelli, S. Y. Woo, L. H. G. Tizei, O. Stéphan, and P. M. Ajayan, Nano Lett. <b>21</b>, 4071 (2021).<br/>[2] S. Susarla, M. H. Naik, D. D. Blach, J. Zipfel, T. Taniguchi, K. Watanabe, L. Huang, R. Ramesh, F. H. da Jornada, and S. G. Louie, ArXiv Prepr. ArXiv2207.13823 (2022).<br/>[3] M. Dandu, J. Hachtel, M. H. Naik, S. Sankar, T. Taniguchi, K. Watanabe, S. G. Louie, F. Jornada, P. Ercius, A. Raja, and S. Susarla, (In Prep.).<br/>[4] S. Susarla, (In Prep).