Visualization of intervalley coherent phase in PtSe2/HOPG heterojunction

TL;DR

This study visualizes the intervalley coherent phase in a PtSe2/hard heterostructure using spectroscopic imaging STM, revealing a modulation pattern linked to the IVC phase and demonstrating its dependence on carrier density and moiré superlattice effects.

Contribution

It provides the first direct visualization of the IVC phase in a heterostructure and explains its origin through a theoretical mechanism involving moiré superlattice effects.

Findings

Visualization of IVC phase via modulation pattern

Correlation between small gap and IVC phase presence

Dependence of modulation pattern on carrier density

Abstract

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 but remains elusive. Here, we successfully visualize the IVC phase in a heterostructure of monolayer PtSe2 on highly oriented pyrolytic graphite. Using spectroscopic imaging scanning tunneling microscopy, we observe a Root3 by Root3 modulation pattern superimposed on the higher-order moire superlattice of the heterostructure, which correlates with a small gap opening around the Fermi level and displays an anti-phase real-space conductance distribution of the two gap edges. Such modulation pattern and small-gap vanish on the heterostructure of monolayer PtSe2 on bilayer-graphene-covered SiC substrate, due to the increased carrier density in the bilayer graphene. We provide a theoretical mechanism that the Root3 by Root3 modulation pattern originates from the IVC phase of few-layer graphene, which is magnified by the higher-order moire superlattice. Our work achieves visualization of the IVC phase, and develops an avenue for its generation and amplification via a moir\'e interface.