Applications of electron energy loss spectroscopy for atomic-scale imaging of exciton and phonon dynamics in quantum materials*

Understanding the structural and electronic correlations such as excitons and phonons in quantum materials is critical for unraveling the fundamental mechanism behind mesoscale phenomena and designing novel device architectures. Normally, the excitons and phonons in different material systems are characterized by optical absorption, photoluminescence, infrared spectroscopy, Raman spectroscopy, and neutron scattering. However, in most of the techniques, the spatial resolution is not enough to comment on the effect of local structural modulations such as defects, moiré patterns, and buried interfaces on the electronic properties of materials. In recent years, correlated electron microscopy and spectroscopy have been used extensively to understand the local structural and electronic properties [1]. In my talk, I will elaborate on how this technique is useful to untangle correlated properties of quantum materials. I will point out two case studies in the field of two-dimensional materials and thin film oxides. In the first case, I would talk about the sensitivity of intralayer excitons to local stacking configurations in twisted transition metal dichalcogenide heterostructures and the effect of excitons on defects in Janus structures [2,3]. In the second case, I would elaborate more on measuring phonons and cyrstal field at the domain walls of ferroelectric oxides [4,5]. At the end of my talk, some of the future challenges involved in electron spectroscopy and some pathways to solve this problem.