Physical properties of novel electronic states related to flat band in twisted two-dimensional quantum materials

Two-dimensional (2D) materials can exhibit novel quantum phenomena and be easily tuned by the external environment, which has made them one of the most attractive topics in condensed matter physics during the recent decades. The moiré superlattice induced by varied stacking geometry can further renormalize the material band structure, resulting in the electronic flat bands. With the help of external fields, one can tune the electron-electron correlated interaction in these flat bands, even control the overall physical properties. In this paper we review the recent researches of novel properties in twisted 2D materials (graphene and transition metal dichalcogenide heterostructure), involving strong correlation effect, unconventional superconductivity, quantum anomalous Hall effect, topological phase, and electronic crystals. We also discuss some open questions and give further prospects in this field.