Realization of one-dimensional electronic flat bands in an untwisted moire superlattice

TL;DR

This paper demonstrates the experimental realization of one-dimensional electronic flat bands in an untwisted moire superlattice through strain engineering, revealing a new approach to create correlated electronic states without layer twisting.

Contribution

It introduces a novel method of generating 1D flat bands in untwisted moire superlattices via strain from lattice mismatch, expanding the design strategies for correlated electronic systems.

Findings

1D flat bands observed near Fermi level in strained Bi(110)/SnSe heterostructure

Strain-induced flat bands occur without layer twist, driven by lattice mismatch

Strain engineering enables control over anisotropic electronic properties

Abstract

Two-dimensional electronic flat bands and their induced correlated electronic interactions have been discovered, probed, and tuned in interlayer regions of hexagonally shaped van der Waals moire superlattices. Fabrication of anisotropic one-dimensional correlated bands by moire interference of 2D, however, remains a challenge. Here, we report an experimental discovery of 1D electronic flat bands near the Fermi level in an anisotropic rectangular moire superlattice composed of in situ grown, vdW stacked two-atomic-layer thick Bi(110) well-aligned on a SnSe(001) substrate. The epitaxial lattice mismatch between the aligned Bi and SnSe zigzag atomic chains causes strong three-dimensional anisotropic atomic relaxations with associated one-dimensional out-of- and in-plane strain distributions that are expressed in electronic bands of the Bi(110) layer, which are characterized jointly by scanning probe microscopy and density functional theory. At the regions of the strongest out-of-plane shear strain, a series of 1D flat bands near the Fermi level are experimentally observed and defined in our calculations. We establish that 1D flat bands can arise in moir\'e superlattices in absence of the relative layer twist, but solely through the lattice strain. We generalize the strategy of utilizing strain in lattice mismatched rectangular hetero-bilayers for engineering correlated anisotropic electronic bands.