Towards optimization of the Josephson diode effect (2501.05671v2)

Abstract: We theoretically study the Josephson diode effect in the junction of singlet superconductors separated by the Rashba system in the in-plane magnetic field perpendicular to the bias current. The coupling energy of two superconductors is formulated under the bias current using a tunneling Hamiltonian with a one-dimensional model. The bias current shifts the Fermi momentum in the Rashba system due to the continuity of the electronic current. Including the shift of Fermi momentum in the coupling energy, it is found that the critical current is asymmetric with respect to the current and the magnetic field, i.e., Josephson diode effect. Depending on a distance between the superconducting electrodes $d$, the Josephson diode effect changes its magnitude and sign. The magnitude is inversely proportional to a band split caused by the spin-orbit interaction. Since $d$ is experimentally controllable, the Josephson diode effect can be optimized by tuning of $d$. Our theory develops a new guiding principle to design the Josephson diode device.