Visualization of Intervalley Coherent Phase in PtSe_{2}/bilayer Graphene Heterojunction

The intervalley coherent (IVC) phase in graphene systems arises from the coherent superposition of wave functions of opposite valleys, whose direct microscopic visualization provides pivotal insight into the emergent physics. Here, we successfully visualize the IVC phase in a heterostructure of monolayer PtSe_{2} and bilayer-graphene (BLG) on graphite. Using spectroscopic imaging scanning tunneling microscopy, we observe a sqrt[3]×sqrt[3] modulation pattern superimposed on the higher-order moiré superlattice of the heterostructure, which correlates with a gap-opening feature around the Fermi level and displays an antiphase real-space conductance distribution of the two gap edges. Such modulation pattern and small gap vanish on the heterostructure of monolayer PtSe_{2} on BLG-covered SiC substrate, due to the increased carrier density in the BLG. We provide a theoretical mechanism that the sqrt[3]×sqrt[3] modulation pattern originates from the IVC phase of BLG, which is magnified by the higher-order moiré superlattice. Our work achieves visualization of the IVC phase, and develops an avenue for its generation and amplification via a moiré interface.