Quantifying electronic band interactions in van der Waals materials using angle-resolved reflected-electron spectroscopy

High electron mobility is one of graphene's key properties, exploited for applications and fundamental research alike. Highest mobility values are found in heterostructures of graphene and hexagonal boron nitride, which consequently are widely used. However, surprisingly little is known about the interaction between the electronic states of these layered systems. Rather pragmatically, it is assumed that these do not couple significantly. Here we study the unoccupied band structure of graphite, boron nitride and their heterostructures using angle-resolved reflected-electron spectroscopy. We demonstrate that graphene and boron nitride bands do not interact over a wide energy range, despite their very similar dispersions. The method we use can be generally applied to study interactions in van der Waals systems, that is, artificial stacks of layered materials. With this we can quantitatively understand the 'chemistry of layers' by which novel materials are created via electronic coupling between the layers they are composed of.We are grateful to Marcel Hesselberth, Daan Boltje and Ruud van Egmond for technical assistance. We thank Charles Kane for fruitful discussions and Kenji Watanabe for supplying the hBN base crystal. This work was supported by the Spanish Ministry of Economy and Competitiveness MINECO (project number FIS2013-48286-C2-1-P) and the Netherlands Organization for Scientific Research (NWO) via an NWO-Groot grant ('ESCHER'), a VIDI grant (680-47-502, S.J. v.d.M.), a VENI grant (680-47-447, J.J.) and by the FOM foundation via the 'Physics in 1D' programme. C.R.D. acknowledges support from NSF grant DMR-1463465