Band alignment and interlayer hybridisation in transition metal dichalcogenide/hexagonal boron nitride heterostructures

TL;DR

This paper investigates how band alignment and hybridisation in TMD/hBN heterostructures influence electronic properties, using DFT calculations and ARPES experiments to understand and correct band energy discrepancies.

Contribution

It introduces a novel scissor operator to correct DFT band alignments in TMD/hBN heterostructures, enabling accurate comparison with experimental ARPES data.

Findings

Hybridisation causes avoided crossings and ghost features in band structure.

DFT underestimates the energy separation between TMD and hBN valence bands.

The scissor operator effectively aligns DFT results with experimental spectra.

Abstract

In van der Waals heterostructures, the relative alignment of bands between layers, and the resulting band hybridisation, are key factors in determining a range of electronic properties. This work examines these effects for heterostructures of transition metal dichalcogenides (TMDs) and hexagonal boron nitride (hBN), an ubiquitous combination given the role of hBN as an encapsulating material. By comparing results of density functional calculations with experimental angle-resolved photoemission spectroscopy (ARPES) results, we explore the hybridisation between the valence states of the TMD and hBN layers, and show that it introduces avoided crossings between the TMD and hBN bands, with umklapp processes opening `ghost' avoided crossings in individual bands. Comparison between DFT and ARPES spectra for the MoSe$_2$/hBN heterostructure shows that the valence bands of MoSe$_2$ and hBN are significantly further separated in energy in experiment as compared to DFT. We then show that a novel scissor operator can be applied to the hBN valence states in the DFT calculations, to correct the band alignment and enable quantitative comparison to ARPES, explaining avoided crossings and other features of band visibility in the ARPES spectra.