Periodic Reporting for period 2 - EuSuper (Superconducting Magnetic RAM for Next Generation of Supercomputers)
Reporting period: 2019-11-15 to 2020-11-14
In this context, EuSuper aims at developing a new generation of nano-sized superconducting non-volatile magnetic memories, with improved efficiency and enhanced functionalities. This is accomplished by : 1) exploiting a wise hybridization between ferromagnetic insulators (FI) and conventional superconducting (S) metals; 2) controlling/tuning the superconducting condensate by an external electrostatic field.
The peculiar behavior of FI/S systems is determined by interfacial quantum phenomena arising at the boundary between the ferromagnetic and superconducting materials. Within a distance from the interface of the order of the superconducting coherence length, the exchange interaction of the FI induces a spin split of the density of states into the S, as per an effective Zeeman splitting generated by an external magnetic field of up to few Tesla (magnetic proximity effect). Besides, the recently demonstrated gate-induced tuning of the superconducting order parameter of fully metallic superconductors may play a key role and introduce new paradigms that ultimately add novel unconventional functionalities and physical insights to S and FI-based nanodevices.
The achievements of this project pave the way for innovative superconducting spintronic applications, i.e. in classical large-scale supercomputing, suitable in all fields of science (solid state physics, artificial intelligence, cryptography, etc.) where increasing speed of calculation and storage are exponentially increasing on demand. Also, from a fundamental physics point of view, the results obtained within the project help in clarifying the interplay between the electrostatic fields and the superconducting condensate as well as the ferromagnetism and superconductivity in FI/S mesoscopic devices and spin-valve. From the technological side, EuSuper counts on small size and scalability of systems to develop an innovative class of superconducting memories ready for the market of incoming next-generation cryogenics supercomputers.
EuSuper is a synergic MSCA that combines the capabilities and expertise of two of the most outstanding and globally recognized research institutions: Massachusetts Institute of Technology (USA) and Consiglio Nazionale delle Ricerche (Italy).
The research objectives (ROs) of the project were the following: i) Growth and characterization of state-of-the-art FI/S-based thin-film heterostructures, (RO1); ii) Miniaturization of FI/S-based hybrid heterostructures, (RO2). iii) Nanoscale engineering of novel FI/S-based ground-breaking superconducting cryogenic RAM prototype (Fig. 1), (RO3).
I successfully achieved the main points of the ROs by focusing all the efforts on the growth and characterization of EuS/Al and GdN/NbN bilayers and more complex stacks (exchange-coupled Josephson junctions). I was also able to develop two specific reliable top-down nanofabrication approaches, especially designed for S and FI/S multilayers. These achievements represent the basis of the miniaturization of S bridges and FI/S mesoscopic heterojunctions, starting from the simplest well-established configurations towards more complex structures. All the above-mentioned accomplishments paved the way towards the miniaturization of the FI/S-based superconducting spin-valves. This will ultimately lead to the fabrication and commercialization of the first reliable nanometric superconducting non-volatile RAM cell, which feasibility was widely demonstrated and published in high impact factor peer-reviewed articles during the return phase at NEST-CNR.
Besides the experimental work, I gave informal/internal seminars and mini-courses (for students and postdocs), which allowed me to transfer my knowledge to the outgoing/return hosts, and enabled the host groups and I to engineer/optimize the integration of their FI/S structure growth recipes to the nanofabrication processes.