Ubiquitous Superconducting Diode Effect Leads to Efficient Superconductor Thin Film Devices for Quantum Circuits

Superconductors continue to exhibit new phenomena on a regular basis despite being extensively studied for over 100 years. Our search for the Majorana bound states in superconducting (SC) Au surface states has led us to rediscover another novel observation - the nonreciprocity of critical supercurrents, called SC diode effect [PRL 131, 027001 (2023)]. Accomplishing unequal supercurrents in SC films in the forward and backward directions enables unprecedented functionalities. We demonstrate strong SC diode effect in conventional SC thin films, such as Nb and V, employing external magnetic fields as small as 1 Oe while in the case of the SC layer interfaced with a ferromagnetic semiconductor EuS, even in the absence of any applied field. SC diode efficiencies reach giant values of over 70%. By careful experimentation and theoretical modeling, we identify that the critical supercurrent nonreciprocity in SC thin films was easily accomplished with asymmetrical vortex edge/surface barriers and the universal Meissner screening current playing a critical role. Our study thus emphasizes the need of great care in the search of exotic SC states harboring finite-momentum Cooper pairing. Moreover, the evolution of SC order parameter, and its intriguing influence on the magnetic ordering will be presented.
SC electronics is essential for energy-efficient quantum and classical high-end SC computing applications. One of the critical long-standing requirements has been the need for the efficient delivery of dc bias current for SC energy-efficient rapid single flux quantum (ERSFQ) circuits which avoids the rise of total dc bias current with the number of cells. This limits the ERSFQ scalability to larger circuit complexities. The non-reciprocal SC circuit elements, for example overcomes such limitations, enabling to achieve scaling and complex circuitry; integrating them in such as SC diode bridge rectifiers, circulators, nonvolatile memory elements etc., and thus fulfill many critical needs. Our recent results on SC rectifiers and SC nonvolatile memory show a pathway with our highly scalable thin film platform for nonreciprocal SC circuits [arXiv:2406.12012]. There is high potential for significantly reducing energy consumption while lowering the decohering thermal and electromagnetic noise in quantum computing.

The work is supported by NSF, AFoSR, ARO, ONR and Lincoln Lab ACC grants.