Promoting and imaging intervalley coherent order in rhombohedral tetralayer graphene on MoS2

TL;DR

This study visualizes and confirms the presence of a robust intervalley coherent order in rhombohedral tetralayer graphene on MoS2 at 77 K, revealing atomic-scale correlated electron patterns using scanning tunnelling microscopy.

Contribution

It provides the first direct microscopic imaging of intervalley coherent order in multilayer rhombohedral graphene, demonstrating the influence of substrate and spin-orbit proximity on correlated phases.

Findings

Observation of atomic-scale <sqrt>3 x <sqrt>3 supercell reconstruction patterns.

Detection of spectroscopic signatures of electronic correlations at flat band fillings.

Identification of substrate-dependent presence of intervalley coherent order.

Abstract

Multilayer rhombohedral graphene (RG) has recently emerged as a new, structurally simple flat-band system, which facilitates the exploration of interaction-driven correlation states with highly ordered electron arrangements. Despite a variety of many-body order behaviors observed in RG by transport measurements, the direct microscopic visualization of such correlated phases in real space is still lacking. Here, we show the discovery of a robust intervalley coherent order, a long-predicted ground state in RG, at 77 K in tetralayer RG placed on MoS2 via imaging atomic-scale spatial reconstruction of wave functions for correlated states. By using scanning tunnelling microscopy, we observe spectroscopic signatures of electronic correlations at partially filled flat bands, where distinct splitting appears. At ~60% and ~70% fillings of the flat bands, we visualize atomic-scale reconstruction patterns with a <sqrt>3 x <sqrt>3 supercell on graphene lattice at liquid nitrogen temperature, which indicates a robust intervalley coherent phase of the interacting electrons. The <sqrt>3 x <sqrt>3 pattern is observed in MoS2-supported RG, while it is absent in hBN-based ones under the same experimental conditions, suggesting the significant influence of spin-orbit proximity effect. Our results provide microscopic insights into the correlated phases in tetralayer RG and highlight the significant potential for realizing highly accessible collective phenomena through Van der Waals proximity.