  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 $\sigma$ 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.
