  Recent experimental work on locally gated graphene layers resulting in p-n
junctions have revealed quantum Hall effect in their transport behavior. We
explain the observed conductance quantization which is fractional in the
bipolar regime and integer in the unipolar regime in terms of quantum Hall edge
modes propagating along and across the p-n interface. In the bipolar regime the
electron and hole modes can mix at the p-n boundary, leading to current
partition and quantized shot noise plateaus similar to those of conductance,
while in the unipolar regime transport is noiseless. These quantum Hall
phenomena reflect the massless Dirac character of charge carriers in graphene,
with particle-hole interplay manifest in mode mixing and noise in the bipolar
regime.
