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Theory of diode effect in d-wave superconductor junctions on the surface of topological insulator

May 2022

We study theoretically the Josephson junction S/FI/S (S: d-wavesuperconductor, FI: ferromagnetic insulator) on the surface of a topologicalinsulator. We find it can show a very large nonreciprocity, i.e., diode effect,by tuning the crystal axis of $d$-wave superconductor and the magnetization inFI. The difference of the upper critical currents $I_c$'s between the positive($I_{c}^{+}$) and negative ($I_{c}^{-}$) directions can be about factor 2,where the current-phase relation can be modified largely from the conventionalone, due to the simultaneous presence of $\sin(\varphi)$, $\sin(2\varphi)$ and$\cos(\varphi)$ components with $\varphi$ being the macroscopic phasedifference between two superconductors. The predicted quality factor $Q$characterizing the diode effect has a strong temperature dependence and itssign is reversed by the change of the direction of the magnetization in FI. Theenhancement of $Q$ at low temperature stems from the Majorana bound states atthe interface. This result can pave a way to realize an efficientsuperconducting diode with low energy cost.

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