Extremely low-frequency oscillations of van Hove singularities induced by sub-Angstrom fluctuations of interlayer spacing in graphene superlattices.

Physical properties of two-dimensional van der Waals (vdWs) structures depend sensitively on both stacking orders and interlayer interactions. Yet, in most cases studied to date, the interlayer interaction is considered to be a static property of the vdWs structures. Here we demonstrate that applying a scanning tunneling microscopy (STM) tip pulse on twisted bilayer graphene (TBG) can induce sub-Angstrom fluctuations of the interlayer separation in the TBG, which are equivalent to dynamic vertical external pressure of about 10 GPa on the TBG. The sub-Angstrom fluctuations of the interlayer separation result in large oscillations of the two van Hove singularities (VHSs) in the TBG. The period of the VHSs oscillations is extremely long, about 500-1000 seconds, attributing to the atomic-thick-film nature of the TBG. Our result provides an efficient method to tune and measure the physical properties of the vdWs structures dynamically.