Abstract
Superconducting diode effect (SDE) is theoretically examined in double quantum dot coupled to three superconducting leads, L, R1 and R2. Lead L is commonly connected to two quantum dots (QD1, QD2) while lead R1 (R2) is connected to QD1 (QD2) only. The phase differences ϕ₁ between leads L and R1 and ϕ₂ between leads L and R2 are tuned independently. The critical current into lead R1 depends on its direction unless ϕ₂ = 0, π, which is ascribable to the formation of Andreev molecule between the QDs. In the absence of electron-electron interaction U in the QDs, the spectrum of the Andreev bound states forms Dirac cones in the ϕ₁-ϕ₂ plane if the energy levels in the QDs are tuned to the Fermi level in the leads. The SDE is enhanced to almost 30\% when ϕ₂ is set to the value at the Dirac points. In the presence of U, the SDE is still observed when U is smaller than the superconducting energy gap in the leads. Our device should be one of the minimal models for the SDE since a similar device with a single QD does not show the SDE.