Gate-tuned Fraunhofer-type Conductance Modulation in Graphene-based Andreev Interferometers

The interplay between superconductivity and the Dirac-fermionic nature of electronic states of graphene leads to unique phase-coherent transport, when graphene is in proximity contact with superconducting electrodes. In this study, we report gate-tuned phase-coherent nonlocal magnetoconductance oscillations in Andreev interferometers consisting of a superconducting Al loop in contact with two ends of a T-shaped mono-layer graphene bar. The conductance oscillations arise from the flux change through the superconducting Al loop, with a gate-dependent Fraunhofer-type modulation of the envelope, which is independent of the sample-specific impurity configuration in the graphene sheet. We confirm that the modulation of envelope is caused by the gate-dependent nonlocal pair coherence along with the change of flux threading the phase-coherent region of graphene between the Al electrodes. The finite-bias effect on the conductance oscillations is also examined in terms of the Onsager-B\"uttiker relation and the BTK-type Andreev reflection probability.