One-dimensional electronic states in a natural misfit structure

TL;DR

This study reveals that interlayer coupling in misfit compounds can significantly alter the electronic properties of one layer type, creating quasi-one-dimensional features, which could enable designing novel electronic states.

Contribution

It demonstrates how interlayer interactions in misfit structures influence electronic band structures, akin to moiré effects, using experimental and theoretical approaches.

Findings

BiSe layers exhibit strong band structure modifications due to NbSe2 layers.

NbSe2 layers' electronic structure remains largely unaffected by BiSe layers.

Modification of bands is linked to atomic and orbital characteristics.

Abstract

Misfit compounds are thermodynamically stable stacks of two-dimensional materials, forming a three-dimensional structure that remains incommensurate in one direction parallel to the layers. As a consequence, no true bonding is expected between the layers, with their interaction being dominated by charge transfer. In contrast to this well-established picture, we show that interlayer coupling can strongly influence the electronic properties of one type of layer in a misfit structure, in a similar way to the creation of modified band structures in an artificial moir\'e structure between two-dimensional materials. Using angle-resolved photoemission spectroscopy with a micron-scale light focus, we selectively probe the electronic properties of hexagonal NbSe$_2$ and square BiSe layers that terminate the surface of the (BiSe)$_{1+\delta}$NbSe$_2$ misfit compound. We show that the band structure in the BiSe layers is strongly affected by the presence of the hexagonal NbSe$_2$ layers, leading to quasi one-dimensional electronic features. The electronic structure of the NbSe$_2$ layers, on the other hand, is hardly influenced by the presence of the BiSe. Using density functional theory calculations of the unfolded band structures, we argue that the preferred modification of one type of bands is mainly due to the atomic and orbital character of the states involved, opening a promising way to design novel electronic states that exploit the partially incommensurate character of the misfit compounds.