Band Gap Opening in Bilayer Graphene-CrCl 3 /CrBr 3 /CrI 3 van der Waals Interfaces.

We report experimental investigations of transport through bilayer graphene (BLG)/chromium trihalide (CrX 3 ; X = Cl, Br, I) van der Waals interfaces. In all cases, a large charge transfer from BLG to CrX 3 takes place (reaching densities in excess of 10 13 cm -2 ), and generates an electric field perpendicular to the interface that opens a band gap in BLG. We determine the gap from the activation energy of the conductivity and find excellent agreement with the latest theory accounting for the contribution of the σ bands to the BLG dielectric susceptibility. We further show that for BLG/CrCl 3 and BLG/CrBr 3 the band gap can be extracted from the gate voltage dependence of the low-temperature conductivity, and use this finding to refine the gap dependence on the magnetic field. Our results allow a quantitative comparison of the electronic properties of BLG with theoretical predictions and indicate that electrons occupying the CrX 3 conduction band are correlated.