Nano-optical imaging of localization phenomena in low-angle twisted bilayer graphene.*

We present evidence for lattice localization physics in the novel reconstructed twisted bilayer graphene (rTBG) system. Here, two graphene layers with an angle smaller than one degree produce the rTBG. In this condition, the carbon atoms rearrange, forming triangular structures composed of solitons and topological points. We use nano-Raman spectroscopy, where a visible-light laser beam is focused on a nano-antenna, to image the rTBG structure. In addition to the first crystalline structure visualization by visible light, this technique provides in-depth spectroscopic information of the rTBG system. Thus, we observe the manifestation of the non-conventional localization of phonons and the already predicted electronic localization. Besides, we also illustrate that the electron-phonon coupling in this system is unique, and its understanding can help elucidate the magic-angle superconductivity. Therefore, our work unravels fascinating phenomena in the fast-developing twistronics field.