  We show nonlinear transport experiments on clean, suspended bilayer graphene
that reveal a gap in the density of states. Looking at the evolution of the gap
in magnetic fields of different orientation, we find that the groundstate is a
spin-ordered phase. Of the three possible gapped groundstates that are
predicted by theory for equal charge distribution between the layers, we can
therefore exclude the quantum anomalous Hall phase, leaving the layer
antiferromagnet and the quantum spin Hall phase as the only possible gapped
groundstates for bilayer graphene.
