Efficient EdgeSuper™: A Breakthrough in Superconducting Diode Technology

The recent research on the LK-99 room-temperature superconductor material by South Korean researchers has sparked global interest. While the Korean research team has since retracted their findings and labs around the world have not confirmed LK-99 as a room-temperature superconductor, its exhibited diamagnetism and potential low-resistance properties have opened a new direction in the study of room-temperature superconducting materials. Recently, a research group at the Massachusetts Institute of Technology (MIT) has developed a superconducting diode device (a low-temperature superconducting device), claiming that this device will enhance the energy and thermal efficiency of electronic products. The related research has been published in the online journal “Physical Review Letters.”

Similar to LK-99 (which is still undergoing a tumultuous process of replication and peer review), the superconducting diode designed by MIT is still in its early stages of development. However, even so, the efficiency of this diode in carrying current (and preventing loss) is already twice that of previous diode architectures, according to the main author of the paper, Jagadeesh Moodera, and his colleagues. There is also ample design space to improve its characteristics.

This development could revolutionize chips and even impact quantum computing. In fact, this development was an accidental discovery as the MIT research team was investigating the “Majorana fermion,” one of the building blocks of topological qubits, a type of quantum bit design yet to be confirmed. The researchers quickly realized that the superconducting diode work inspired by Majorana fermions could easily be translated into the realm of classical (non-quantum) circuitry.

Diodes are a critical foundational part of any chip and an essential component of circuit design. While transistors are used to amplify input signals from low-resistance circuits to high-resistance circuits within a chip, diodes typically convert alternating current (AC) to direct current (DC). Moreover, diodes possess the characteristic of allowing current to flow in only one direction, achieved through the difference in the conductive behavior of two types of charge carriers (electrons and holes). This makes them widely applicable in electronic products.

Due to the strong limitations imposed by heat generated from electrical losses on chip design (a bottleneck that transistor designs and new cooling technologies are increasingly complex in dealing with), the benefits of lossless diodes in improving computational and thermal efficiency should not be underestimated.

Superconducting diodes can also be used in sensors and other devices. However, achieving superconducting diodes is more challenging since there is only one type of charge carrier—electrons in what’s known as Cooper pairs. In 2020, researchers demonstrated diode effects in superconducting devices made from layered materials, requiring precise stacking, strong spin-orbit coupling, and a unique form of Cooper pairing. Now, the superconducting diodes developed by the MIT research team are not only more efficient but also simpler in design.

The team’s diode design consists of a narrow strip of niobium or vanadium. Unlike most single-element superconductors, both niobium and vanadium are Type II superconductors, meaning that applying a sufficiently strong magnetic field induces the formation of supercurrent vortices, which rotate with the same sense. Moodera and his colleagues applied this field vertically to the surface of their device, inducing vortices within the strip as well as edge supercurrents (known as Meissner currents) along the strip’s edge. From above, a current flows to the right along one edge (“forward” direction) and to the left along the other edge (“reverse” direction). Then, researchers sent external current—forward and reverse—at the end of the strip and measured the net current in each case.

The MIT research team showed that tiny differences between the edge currents of the diode devices can be optimized (by adding serrated edges or applying other deformations). This is why the design is still to be optimized: the potential variations in design are vast, and there is plenty of time to find the best asymmetric configuration.

This research highlights how even microscopic differences in materials can lead to disproportionate outcomes. These diodes also exhibit superconducting features, such as the Meissner effect and the ability to lock in a pre-existing magnetic field (known as flux pinning).

Philip Moll (Director at the Max Planck Institute for the Structure and Dynamics of Matter, Germany, not involved in this research) stated in an interview with SciTechDaily that the MIT team’s paper demonstrates the significant significance of observing large diode effects in single-element superconductors due to their simplicity, making applications easier and more scalable. “What’s remarkable about Moodera and his colleagues’ work is that they achieved record efficiency without even trying much.” However, he also pointed out that “their structure is far from optimized.”

Importantly, the team suggests that their superconducting diodes are robust and durable, capable of operating over a wide range of temperatures while potentially opening doors for new technologies and designs. Engineers state that the design of these diodes is simple and compatible, easily scalable to millions of diodes that can be produced on a single silicon wafer.