Coherent multiple Andreev reflections and current resonances in SNS quantum point contacts - art. no. 144504

We study coherent multiple Andreev reflections in ballistic superconductor- normal conductor-superconductor junctions with a quantum point contact in t he normal region of the junction (superconductor-normal region-quantum poin t contact-normal region-superconductor) with arbitrary transparency. The pr esence of superconducting bound states in these junctions gives rise to gre at enhancement of the subgap current. The effect is most pronounced in low- transparency junctions, D much less than1, and in the interval of applied v oltage Delta /2 <eV<2 Delta, where the amplitude of the current structures is proportional to the first power of the junction transparency D. The reso nant current structures consist of steps and oscillations of the two-partic le current and also of multiparticle resonance peaks. The positions of the two-particle current structures have a pronounced temperature dependence, w hich scales with Delta (T), while the positions of the multiparticle resona nces have a weak temperature dependence, being mostly determined by the jun ction geometry. Despite the large, resonant two-particle current, the exces s current at large voltage is small and proportional to D-2.