  We use the half-filled zeroth Landau level in graphene as a regularization
scheme to study the physics of the SO(5) non-linear sigma model subject to a
Wess-Zumino-Witten topological term in 2+1 dimensions. As shown by Ippoliti et
al. [PRB 98, 235108 (2019)], this approach allows for negative sign free
auxiliary field quantum Monte Carlo simulations. The model has a single free
parameter, $U_0$, that monitors the stiffness. Within the parameter range
accessible to negative sign free simulations, we observe an ordered phase in
the large $U_0$ or stiff limit. Remarkably, upon reducing $U_0$ the
magnetization drops substantially, and the correlation length exceeds our
biggest system sizes, accommodating 100 flux quanta. The implications of our
results for deconfined quantum phase transitions between valence bond solids
and anti-ferromagnets are discussed.
