Visualizing broken symmetry states in the zeroth Landau level of the graphene quantum Hall system

In graphene, the combination of electron spin and two equivalent sublattice atoms results in a four-fold degeneracy of Landau levels. A number of competing quantum Hall isospin states inside the four-fold degenerate zeroth landau level of graphene have been suggested based on macroscopic transport measurements. Here we observe the broken symmetry states of the zeroth Landau level in graphene with Kelvin Probe Force Microscopy (KPFM) by using a millikelvin scanning probe microscope coupled with qPlus sensor. The field dependence of the energy difference between isospin states is suggestive of transitions between isospin configurations at certain magnetic field values. In addition, we show how the quantum Hall edge channels of zeroth Landau level spatially develop and disperse at the edge of Hall bar.