Fig. 1.

MAR. Illustrations of the leading processes contributing to the current as function of bias. In general, for $2\mathrm{\Delta }/\left(n-1\right)>e{V}_{SD}>2\mathrm{\Delta }/n$ the leading charge contribution to the current is ne. An electron-like quasiparticle is denoted by a full circle, whereas a hole-like quasiparticle is denoted by an empty circle. (A) When the bias is larger than the energy gap, $e{V}_{SD}>2\mathrm{\Delta }$, the leading process is a single-path tunneling of single quasiparticles from the full states (Left) to the empty states (Right). This current is proportional to the transmission coefficient t. Higher-order MAR process (dashed box), being responsible for tunneling of Cooper pairs, is suppressed as t². (B) For $2\mathrm{\Delta }>e{V}_{SD}>\mathrm{\Delta }$, the main charge contributing to the current is 2e with probability t². (C) For $\mathrm{\Delta }>e{V}_{SD}>2\mathrm{\Delta }/3$, the main charge contributing to the current is 3e with probability t³.