Imaging the many-body wavefunctions in magic-angle graphene*

Magic-angle twisted bilayer graphene (MATBG) hosts a set of flat electronic bands that produce a wide variety of correlated ground states including superconductors, correlated insulators, and magnetic topological phases. Our understanding of these phases has thus far been hampered by the lack of microscopic, atomic-scale information on them. In this talk, I will discuss how we use high-resolution scanning tunneling microscopy (STM) measurements to study the wavefunctions of these correlated phases. STM images reveal distinct symmetry-breaking patterns with a sqrt(3) x sqrt(3) superperiodicity on the graphene atomic lattice. To understand these patterns, we develop a symmetry-based analysis to visualize the images in terms of a set of complex-valued order parameters. At the correlated insulators at fillings ±2 electrons per moiré unit cell, comparison with theoretical candidates reveals a close match with the proposed incommensurate Kekulé spiral order in samples with typical values of interlayer strain, while in ultralow-strain samples, our data have local symmetries resembling the time-reversal symmetric intervalley coherent phase. These symmetry-based techniques can be further applied to other phases in MATBG, graphene systems, and potentially other material systems.