Strong structural and electronic coupling in metavalent PbS moire superlattices

TL;DR

This paper demonstrates the synthesis of moire superlattices in PbS with strong chemical bonding, revealing twist-angle-dependent electronic structures and flat bands, opening new avenues beyond van der Waals twistronics.

Contribution

It introduces a novel method to create strongly bonded PbS moire superlattices with tunable electronic properties, contrasting with traditional weakly bonded systems.

Findings

Strong metavalent coupling causes structural reconstruction.

Flat bands emerge at small twist angles.

Localized states resemble quantum dots.

Abstract

Moire superlattices are twisted bilayer materials, in which the tunable interlayer quantum confinement offers access to new physics and novel device functionalities. Previously, moire superlattices were built exclusively using materials with weak van der Waals interactions and synthesizing moire superlattices with strong interlayer chemical bonding was considered to be impractical. Here using lead sulfide (PbS) as an example, we report a strategy for synthesizing of moire superlattices coupled by strong chemical bonding. We use water-soluble ligands as a removable template to obtain free-standing ultra-thin PbS nanosheets and assemble them into direct-contact bilayers with various twist angles. Atomic-resolution imaging shows the moire periodic structural reconstruction at superlattice interface, due to the strong metavalent coupling. Electron energy loss spectroscopy and theoretical calculations collectively reveal the twist angle26 dependent electronic structure, especially the emergent separation of flat bands at small twist angles. The localized states of flat bands are similar to well-arranged quantum dots, promising an application in devices. This study opens a new door to the exploration of deep energy modulations within moire superlattices alternative to van der Waals twistronics.