Scanning tunneling microscopy study of twisted Bernal-stacked tetralayer graphene

Twisted multilayer graphene provides an unprecedented platform for studying strongly correlated and topological physics, such as twisted monobilayer graphene (TMBG) featured with electric-field tunable superconductivity. Adding an extra layer to TMBG, twisted tetralayer graphene emerges with more fascinating correlated phases related to crystal symmetry and band structure. In this study, by using scanning tunneling microscope, we thoroughly investigated twisted Bernal-stacked tetralayer graphene with a small twist angle in three distinct configurations: a twist between monotrilayer (A/BAB), bibilayer (AB/AB), and trimonolayer (ABA/B). All three types host almost the same twist angle induced by as-grown grain boundaries. We detected two distinct scanning tunneling spectroscopy spectra on the A/BAB- and ABA/B-type tetralayer graphene, indicative of mirror-symmetry breaking. Notably, both flat and linear bands coexist in the tetralayer system with a small twist angle, which supports emerging correlated phases. Moreover, our result revealed layer-dependent distribution of local density of states assigned to the flat and linear bands in twisted tetralayer graphene. Intriguingly, the flat-band localization becomes weakened as the twisted interface recedes from the top to bottom layers. This work not only sheds light on structural and electronic properties of twisted tetralayer graphene in distinct configurations, but also opens up further opportunities in understanding correlated physics in twisted multilayer graphene system.