Two-dimensional charge order stabilized in clean polytype heterostructures

TL;DR

This paper demonstrates a novel endotaxial polytype engineering method to stabilize two-dimensional charge density waves in van der Waals heterostructures, enabling the observation of fragile quantum states in clean 2D materials.

Contribution

It introduces endotaxial polytype engineering as a new approach to realize and stabilize 2D quantum states in van der Waals heterostructures, overcoming disorder effects.

Findings

Stabilization of commensurate long-range 2D charge density waves

Observation of a metal-insulator transition at ~350 K

Mapping of charge density wave formation using electron microscopy

Abstract

Compelling evidence suggests distinct correlated electron behavior may exist only in clean 2D materials such as 1T-TaS2. Unfortunately, experiment and theory suggest that extrinsic disorder in free standing 2D layers disrupts correlation-driven quantum behavior. Here we demonstrate a route to realizing fragile 2D quantum states through endotaxial polytype engineering of van der Waals materials. The true isolation of 2D charge density waves (CDWs) between metallic layers stabilizes commensurate long-range order and lifts the coupling between neighboring CDW layers to restore mirror symmetries via interlayer CDW twinning. The twinned-commensurate charge density wave (tC-CDW) reported herein has a single metal--insulator phase transition at ~350 K as measured structurally and electronically. Fast in-situ transmission electron microscopy and scanned nanobeam diffraction map the formation of tC-CDWs. This work introduces endotaxial polytype engineering of van der Waals materials to access latent 2D ground states distinct from conventional 2D fabrication.