Quantized conductance with nonzero shot noise as a signature of Andreev edge state
Manas Ranjan Sahu, Arup Kumar Paul, Jagannath Sutradhar, Kenji Watanabe, Takashi Taniguchi, Vibhor Singh, Subroto Mukerjee, Sumilan Banerjee, Anindya Das
Abstract
Electrical conductance measurements have a limited scope in identifying Andreev edge states (AESs), which form the basis for realizing various topological excitations in quantum Hall (QH)--superconductor (SC) junctions. To unambiguously detect AESs, we measure shot noise along with electrical conductance in a graphene-based QH-SC junction at integer filling $\ensuremath{\nu}=2$. Remarkably, we find that the Fano factor of shot noise approaches half when the bias energy is less than the superconducting gap ($2\mathrm{\ensuremath{\Delta}}$), whereas it is close to zero above $2\mathrm{\ensuremath{\Delta}}$. This is striking, given that, at the same time, the electrical conductance remains quantized at $2{e}^{2}/h$ within and above $2\mathrm{\ensuremath{\Delta}}$. A quantized conductance is expected to produce zero-shot noise due to its dissipationless flow. However, at a QH-SC interface, AESs carry the current in the zero-bias limit and an equal mixing of electron- and holelike states produces half of the Poissonian shot noise with quantized conductance. The observed results are in accord with our detailed theoretical calculations of electrical conductance and shot noise based on the nonequilibrium Green's function method in the presence of disorder. Our results pave the way in using shot noise as a detection tool in the search for exotic topological excitations in QH-SC hybrids.