Magnetointerferometry of multiterminal Josephson junctions

We report a theoretical study of multiterminal Josephson junctions under the influence of a magnetic field $B$. We consider a ballistic rectangular two-dimensional metal $N_0$ connected by the edges to the left, right, top, and bottom superconductors $S_L$, $S_R$, $S_T$, and $S_B$, respectively. We numerically calculate in the large-gap approximation the critical current $I_c$ versus $B$ between the left and right $S_L$ and $S_R$ for various aspect ratios, with the top and bottom $S_T$ and $S_B$ playing the role of superconducting mirrors. We find the critical current $I_c$ to be enhanced by orders of magnitude, especially at long distance, due to the phase rigidity provided by the mirrors. We obtain magnetic oscillations resembling those of a superconducting quantum interference device. With symmetric couplings, the self-consistent superconducting phase variables of the top and bottom mirrors take the values 0 or $\pi$, as for emerging Ising degrees of freedom. We propose a simple effective Josephson junction circuit model that is compatible with these microscopic numerical calculations. From the $I_c\left(B\right)$ patterns we infer where the supercurrent flows in various device geometries. In particular in the elongated geometry, we show that the supercurrent flows between all pairs of contacts, which allows exploring the full phase space of the relevant phase differences.