Integrating Superconducting and Spintronics Devices for Low-Power and High-Speed Operation and Brain-Inspired Computing

There is a growing need to address the power consumption in future computer technologies, beyond the traditional approach of a continued increase in a number of scaled-down transistors. Superconducting electronics offers promising energy-efficient alternatives, even after including the cost of cooling. The key element of superconducting electronics is the Josephson junction, recognized by the 1973 Nobel Prize in Physics.

In this junction two superconductors are separated by the nonsuperconducting region, but zero-resistance charge current can still flow across the whole device. However, the lack of suitable memories remains a key challenge and prevents the integration of superconducting logic and memory. To overcome this limitation and unlock potential for brain-inspired computing, it is proposed to integrate advances from the field of spintronics where information is represented by electron spin and by its proxy, the direction of magnetization.

Ferromagnets such as iron or cobalt have a finite magnetization, resulting from a spin imbalance: a different number of electron spins is oriented with or against the magnetization axis. Ideal for memory, this magnetization persists without an outlet power, just as the magnet is attracted to the fridge. Unlike magnets, common superconductors have spin balance, they are characterized by a collection of paired electros with spins of opposite directions.

Bringing a magnet with its spin imbalance next to a superconductor destroys the spin balance and superconductivity. The proposed research reveals that by engineering spin-orbit coupling it is possible to transform superconductors to have paired electrons of equal spins thereby ensuring their coexistence with magnets for integrating memory with logic.

The findings of the proposed research will be closely integrated with the outreach efforts, recognizing that a vast majority of public-school students have minimal or no exposure to physical sciences adversely affecting the subsequent enrolment in STEM disciplines. Summer Workshops will be organized on: Applications of Magnetism and Super-conductivity covering topics on spintronics, motors, medical imaging, Maglev trains, and biomagnetism.

As a part of the annual SPIE: Optics&Photonics Conference, Superconducting Spintronics Symposia will be organized to bridge the gap between the spintronics and superconducting applications.

The hallmark of Josephson junctions is the phase-coherence with the corresponding current-phase relations, where dissipationless charge current can flow even at zero applied bias. Dynamical operation of Josephson junctions resembles oscillations of a damped pendulum. Ultrafast oscillations, analogous to the full-circle rotation of a pendulum, can be switched quickly at ~1 ps, dissipate only 0.1 aJ per switch, while producing current pulses that travel at 1/3 of the speed of light.

The proposed work reveals how these properties can enable potentially transformative spintronic devices in which the presence of spin-orbit coupling and magnetic regions would alter dissipationless currents to also carry spin and provide a seamless integration of logic and memory. Such Josephson junctions therefore serve both as an element of logic and of memory: logic is implemented through ultrafast current pulses, while the memory is encoded through the magnetization orientation with the readout based on the superconducting phase.

The tunability of current-phase relations with spin-orbit coupling also offers unexplored opportunities in brain-inspired computing and artificial neural networks, relying on phase-controlled current pulses. Josephson junction devices will be examined through comprehensive modeling of their superconducting and magnetic properties, while the precise form of spin-orbit coupling will be calculated from the first-principles atomistic studies.

These results will be experimentally verified through collaborations with several groups fabricating Josephson junctions. The findings of the proposed research will be closely integrated with the outreach efforts, recognizing that a vast majority of public-school students have minimal or no exposure to physical sciences adversely affecting the subsequent enrolment in STEM disciplines.

The PI will organize Summer Workshops: Applications of Magnetism and Super-conductivity covering topics on spintronics, motors, medical imaging, Maglev trains, and biomagnetism. As a part of the annual SPIE: Optics+Photonics Conference, the PI will organize Superconducting Spintronics Symposia to bridge the gap between the spintronics and superconducting applications.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.