Quantum magnetotransport oscillations in graphene nanoribbons coupled to superconductors

Magnetotransport properties of zigzag and armchair graphene nanoribbons that are in contact with superconductors are investigated using a tight-binding model. The cyclotron orbital motion together with the quantum interference under the coexistence of Andreev and normal reflections gives rise to a number of oscillations in characteristic magnetic-field regimes when the superconducting coupling is weak. The oscillations become irregular and/or suppressed as the coupling is made strong. The period of the oscillations differs from that when a nonrelativistic two-dimensional electron gas is employed rather than the graphene sheet. The modifications of the oscillations are attributed to the phase shift associated with the reflection from the graphene-superconductor interface. The presence of a magnetic field suppresses the quantum blocking of Andreev transmission, which occurs for the edge mode of zigzag nanoribbons, in the same way regardless of it being induced by the Andreev retro- or specular reflection.

Automated summary

The study reveals that the oscillations in magnetic field regimes of zigzag and armchair graphene nanoribbons in contact with superconductors become irregular and/or suppressed as the coupling strength increases. These oscillations differ from those of a nonrelativistic two-dimensional electron gas and are attributed to the phase shift at the graphene-superconductor interface. Additionally, the presence of a magnetic field suppresses the quantum blocking of Andreev transmission in zigzag nanoribbons, regardless of the type of reflection involved.