Supercurrent reversal in quantum dots induced by spin-pump effects

The spin-pump effects caused by the rotating magnetic field on the supercurrent in a superconductor-quantum-dot-superconductor system are studied theoretically. By tuning the magnetic-field strength, the sign of the supercurrent can be changed from positive to negative, which results in the π -junction transition. The π -junction transition can also be tuned by the quantum dot energy level. The tunable π -junction transition is interpreted in the picture of the current carrying density of states, which clearly shows the enhancement, suppression, and reversion of the supercurrent.