Novel electronic structures from anomalous stackings in NbS$_2$ and MoS$_2$

TL;DR

This study reveals that anomalous stacking sequences in NbS₂ and MoS₂ lead to unexpected 2D electronic states, expanding understanding of how stacking variations influence electronic properties in layered materials.

Contribution

It demonstrates the existence of novel stacking configurations in NbS₂ and MoS₂ that produce unique electronic structures not seen in typical bulk polytypes.

Findings

Minority regions show 2D electronic states instead of 3D bands.

Discovery of exotic 4Ha stacking with quasi-2D valence band.

Presence of multiple stacking types within the same sample.

Abstract

We show that in some transition metal dichalcogenides, minority regions of the cleaved sample surfaces show - unexpectedly and anomalously - a finite number of 2D electronic states instead of the expected 3D valence bands. In the case of NbS\textsubscript{2}, in addition to the typical spectrum associated with bulk 2Ha stacking, we also find minority regions with electronic structures consistent with few-layers of 3R stacking. In MoS\textsubscript{2} we find areas of both bulk 2Hc and 3R stackings, and regions exhibiting finite-layer quantisation of both types. We further find evidence for a more exotic 4Ha stacking of MoS\textsubscript{2}, in which the valence band maximum is quasi-2D. The results highlight how variation of the interlayer stacking of van der Waals materials beyond the commonly-reported bulk polytypes can yield novel electronic structures.