Tiancong Zhu1,2
University of California, Berkeley1,Lawrence Berkeley National Laboratory2
Tiancong Zhu1,2
University of California, Berkeley1,Lawrence Berkeley National Laboratory2
Twisting and stacking two-dimensional van der Waals materials provides a versatile platform for investigating emergent quantum phases of matter driven by strong correlation and non-trivial topology. One example is twisted monolayer-bilayer graphene (tMBLG), where correlated Chern insulating states with electrically switchable magnetic order have been recently demonstrated in transport measurements. I will discuss scanning tunneling microscopy (STM) measurements where high spatial resolution provides new insight into the interplay between correlation, topology, and local structural distortion in determining the electronic and magnetic properties of tMBLG. Our STM spectroscopy (STS) provides evidence for the formation of interaction-driven energy gaps at both ½- and ¾- filling of a moiré mini-band in tMBLG. Magnetic-field-dependent STS measurements further indicate a non-zero total Chern number of <i>C</i><sub>tot</sub> = ±2 for the ¾-filled correlated insulating state. In certain regions of the sample, we find that the sign of <i>C</i><sub>tot</sub> can be reversed via electrostatic gating in a finite magnetic field, consistent with the electrically switchable magnetic order reported in previous transport studies. This electrical reversibility, however, is not universal and depends strongly on the local hetero-strain (relative strain between the monolayer and bilayer graphene) in tMBLG. The electrical switching of magnetic order appears to result from a competition between the orbital magnetization of filled bulk bands and chiral edge states that is highly sensitive to strain-induced distortion of the moiré superlattice. Our finding illustrates the critical role of local environmental factors in shaping correlation and topology in twisted two-dimensional systems.