Supercurrent and Superconducting Diode Effect in Parallel Double Quantum Dots with Rashba Spin-Orbit Interaction

We study theoretically the supercurrent and the superconducting diode effect (SDE) in a structure comprising parallel-coupled double quantum dots (DQDs) sandwiched between two superconductor leads in the presence of a magnetic flux. The influence of the Rashba spin-orbit interaction (RSOI), which induces a spin-dependent phase factor in the dot-superconductor coupling strength, is taken into account by adopting the nonequilibrium Green's function technique. This RSOI-induced phase factor serves as a driving force for the supercurrent in addition to the usual superconducting phase difference, and it leads to the system's left/right asymmetry. Correspondingly, the magnitude of the positive and negative critical currents become different from each other: the so-called SDE. Our results show that the period, magnitude, and direction of the supercurrents depend strongly on the RSOI-induced phase factor, dots' energy levels, interdot coupling strengths, and the magnetic flux. In the absence of magnetic flux, the diode efficiency is negative and may approach -2, which indicates the perfect diode effect with only negative flowing supercurrent in the absence of a positive one. Interestingly enough, both the sign and magnitude of the diode efficiency can be efficiently adjusted with the help of magnetic flux, the dots' energy levels and the interdot coupling strength and thus provide a controllable SDE by rich means, such as gate voltage or host materials of the system.