Spontaneous interlayer compression in commensurately stacked van der Waals heterostructures

TL;DR

This study reveals that commensurate stacking in van der Waals heterostructures causes interlayer compression due to polarization interactions, affecting structural and electronic properties, with implications for heterostructure design.

Contribution

It provides a detailed analysis of how idealized commensurate stacking influences interlayer spacing and electronic properties in transition metal dichalcogenide heterostructures, highlighting the role of polarization interactions.

Findings

Strong interlayer compression in heterostructures with dissimilar chalcogens.

Polarization interactions increase without full charge transfer.

Incommensurate stacking stabilizes charge density wave modes.

Abstract

Interest in layered two dimensional materials, particularly stacked heterostructures of transition metal dichalcogenides, has led to the need for a better understanding of the structural and electronic changes induced by stacking. Here, we investigate the effects of idealized heterostructuring, with periodic commensurate stacking, on the structural, electronic, and vibrational properties, when compared to the counterpart bulk transition metal dichalcogenide. We find that in heterostructures with dissimilar chalcogen species there is a strong compression of the inter-layer spacing, compared to the bulk compounds. This compression of the heterostructure is caused by an increase in the strength of the induced polarization interaction between the layers, but not a full charge transfer. We argue that this effect is real, not due to the imposed commensurability, and should be observable in heterostructures combining different chalcogens. Interestingly, we find that incommensurate stacking of Ti-based dichalcogenides leads to the stabilization of the charge density wave phonon mode, which is unstable in the 1T phase at low temperature. Mixed Ti- and Zr-heterostructures are still unstable, but with a charge density wave or a ferroelectric instability.