We address the question about the origin of the $\frac{1}{2}(e^2/h)$ conductance plateau observed in a recent experiment on an integer quantum Hall (IQH) film covered by a superconducting (SC) film. Since one-dimensional (1D) chiral Majorana fermions on the edge of the above device can give rise to the half quantized plateau, such a plateau is regarded as conclusive evidence for the chiral Majorana fermions. However, in this Letter we give another mechanism for the $\frac{1}{2}(e^2/h)$ conductance plateau. We find the $\frac{1}{2}(e^2/h)$ conductance plateau to be a general feature of a good electric contact between the IQH film and the SC film, and cannot distinguish the existence or the nonexistence of 1D chiral Majorana fermions. We also find that the contact conductance between a superconductor and an IQH edge channel has a non-Ohmic form ${\sigma }_{\mathrm{SC}\text{−}\mathrm{Hall}}\propto V^2$ in the $k_{B}T\ll eV$ limit, if the SC and IQH bulks are fully gapped.

• Received 27 August 2017

DOI:https://doi.org/10.1103/PhysRevLett.120.107002