Josephson effect in graphene-based multi-terminal Josephson junctions*

A multi-terminal Josephson junction (MTJJ) consists of n (>2) independent superconductors coupled via a normal conductor. The supercurrent flowing in a MTJJ is a function of the (n-1) independent phase differences between the terminals. The phases act as quasimomenta and the resulting band structure may exhibit topological states and Weyl nodes in (n-1) dimension. A prior experiment (Phys. Rev. X 10, 031051) used InAs-based MTJJs involving multiple two-terminal Josephson junctions (2TJJs) coupled through a normal region. Here we studied a different geometry wherein Al terminals are edge-contacted to graphene without forming any 2TJJs. We measured the critical current contours (CCCs) and multiple Andreev reflections as  functions of magnetic field and carrier concentration. In contrast to the prior results, we observed that the CCC expands (shrinks) with increasing carrier concentration (magnetic field) without deformation. We will discuss possible interpretations of our results.