A mechanism of 1/2 e^2/h conductance plateau without 1D chiral Majorana fermions*

We address the question about the origin of the 1/2 e^2/h
conductance plateau observed in a recent experiment on an integer quantum Hall
(IQH) film covered by a superconducting (SC) film. Since 1-dimensional (1D)
chiral Majorana fermions on the edge of the above device can give rise to the
half quantized plateau, such a plateau was regarded as a smoking-gun evidence
for the chiral Majorana fermions. However, in this paper we give another
mechanism for the 1/2 e^2/h conductance plateau. We find the
1/2 e^2/h conductance plateau to be a general feature of a good
electric contact between the IQH film and SC film, and cannot distinguish the
existence or the non-existence of 1D chiral Majorana fermions. We also find
that the contact conductance between SC and an IQH edge channel has a non-Ohmic
form, i.e., proportional to V^2, in k_BT<< eV limit, if the SC and
IQH bulks are fully gapped.