  We report on magneto-transport measurements on low-density, large-area
monolayer epitaxial graphene devices grown on SiC. We show that the zero-energy
Landau level (LL) in monolayer graphene, which is predicted to be magnetic
field ($B$)-independent, can float up above the Fermi energy at low $B$. This
is supported by the temperature ($T$)-driven flow diagram approximated by the
semi-circle law as well as the $T$-independent point in the Hall conductivity
$\sigma_{xy}$ near $e^2/h$. Our experimental data are in sharp contrast to
conventional understanding of the zeroth LL and metallic-like behavior in
pristine graphene prepared by mechanical exfoliation at low $T$. This
surprising result can be ascribed to substrate-induced sublattice symmetry
breaking which splits the degeneracy of the zeroth Landau level. Our finding
provides a unified picture regarding the metallic behavior in pristine graphene
prepared by mechanical exfoliation, and the insulating behavior and the
insulator-quantum Hall transition in monolayer epitaxial graphene.
