Unravelling the Topological Edge States of Twisted Bilayer Graphene

Stacking two slightly lattice-mismatched or relatively twisted two-dimensional (2D) materials gives rise to an unexpected richness of physical phenomena due to the emerging moiré pattern. In particular, twisted-bilayer graphene (t-BLG) has recently been shown to host strongly correlated phases as well as unconventional superconductivity [1, 2]. While recent studies have hinted at the non-trivial topology of the moiré bands [3, 4], direct experimental observations of the topological edge states are still conspicuously missing. Herein, using superconducting quantum interference, we reconstruct the real-space current distribution in t-BLG Josephson junctions (JJs) and reveal the presence of conductive edge states when the Fermi level is placed in the superlattice induced band gaps. These results suggest the non-trivial topology of t-BLG and lay the groundwork to understand and exploit the edge states in moiré materials. [1] Cao, Y.; Fatemi, V.; Fang, S.; Watanabe, K.; Taniguchi, T.; Kaxiras, E.; Jarillo-Herrero, P. Nature 2018, 556, (7699), 43. [2] Cao, Y., Fatemi, V., Demir, A., Fang, S., Tomarken, S. L., Luo, J. Y., ... & Jarillo-Herrero, P. (2018). Nature, 556(7699), 80-84. [3] Park, M. J., Kim, Y., Cho, G. Y., & Lee, S. (2019). Physical review letters, 123(21), 216803. [4] Ma, C.; Wang, Q.; Mills, S.; Chen, X.; Deng, B.; Yuan, S.; Li, C.; Watanabe, K.; Taniguchi, T.; Du, X.; Zhang, F.; Xia, F. Nano Letters 2020, 20, (8), 6076-6083.