Design of a Josephson diode based on double magnetic impurities

We theoretically propose a universal superconducting diode device based on double magnetic impurities which are coupled to the connection region of the Josephson junction. The positive and negative currents flowing across the junction can generate opposite magnetic fields, flipping the magnetic moment of the side magnetic impurity to the opposite directions, and in turn, the two impurities will have different impacts on the opposite currents. This results in the phenomenon that the positive and negative critical currents are unequal, referred to as the superconducting diode effect (SDE). Using the nonequilibrium Green's function method (NEGF), we obtain the direction-dependent critical currents. We confirm the emergency of the SDE and demonstrate the dependence of the superconducting diode efficiency on a range of parameters including the magnitude, the direction, and the position of the magnetic moment. In addition, we systematically analyze the symmetry relations of the nonreciprocity in our system. Our proposal has high practicability by avoiding the demand on the external magnetic field, the Cooper pair momentum, and the spin-orbit coupling. Our approach opens up new possibilities for the development of nonreciprocal electronic circuits and provides an alternate perspective on the advancement of superconducting devices.