  We report a double-layer electronic system made of two closely-spaced but
electrically isolated graphene monolayers sandwiched in boron nitride. For
large carrier densities in one of the layers, the adjacent layer no longer
exhibits a minimum metallic conductivity at the neutrality point, and its
resistivity diverges at low temperatures. This divergence can be suppressed by
magnetic field or by reducing the carrier density in the adjacent layer. We
believe that the observed localization is intrinsic for neutral graphene with
generic disorder if metallic electron-hole puddles are screened out.
