Expeditions: DISCoVER: Design and Integration of Superconducting Computation for Ventures beyond Exascale Realization

It is proposed to fabricate and investigate various types of magnetic Josephson junctions (MJJs) with the goal of evaluating their suitability as novel elements in the superconducting circuits. Although hybrid Josephson junctions (JJs) involving magnetic layers have been a subject of intensive study in recent years, very little is done to implement these devices into practically useful circuits, typically because of some drawbacks of MJJs – a low Josephson critical current, Ic, and low critical voltage, Vc. Our effort will focus on improving these parameters, specifically by using multilayer F/N barriers (where F and N denote a ferromagnetic material and a normal (non-magnetic) metal, respectively. Our recent work on such structures has revealed some unusual behaviors including a self-shunting property and an oscillatory dependence of Ic vs. externally applied magnetic field; the latter may be evidence for a substantial deviation of the current-phase relation (CPR) from a sinusoidal one in these junctions. We believe that both  and 0- junctions can be developed based on such JJs with multilayer F/N barriers, as our preliminary results indicate. The second focus of the proposed study is optimization of the SIsFS junctions, where s is a thin (on the order of the coherence length) superconductor. It has been shown that such junctions have a large Vc and a high critical current density, and, at the same time, can be designed to have a 0- transition and a strong second harmonic component in the CPR. Also, such junctions can serve as memory elements. At present, such junctions have mostly been studied theoretically; more extensive experimental study is necessary to obtain JJs with desired properties (i.e., clear -JJ behavior and 2-JJ behavior), which is one of the goals of the NU part of the DISCoVER project. The proposed work has a high potential for making important contributions to the fundamental science surrounding the interaction between the su