A group of researchers from MIT and their peers have created a straightforward superconducting gadget that might transmit current through electrical devices a lot more effectively than is now achievable. As a result, the novel switch-like diode has the potential to significantly lower the energy requirements of high-power computer systems. This is an urgent problem that is expected to grow in importance over time. The diode is more than twice as efficient as comparable ones that have been reported by others, while being in the early phases of research. It could even be crucial to upcoming quantum computing innovations.
A simple superconducting gadget developed by MIT researchers and associates might transport current through electronic devices far more effectively than is now achievable. The novel diode, a type of switch, might thereby significantly reduce the amount of energy required in high-power computer systems, a significant issue that is anticipated to get much worse. The diode is more than twice as efficient as comparable ones that have been reported by others, while being in the early phases of research. It could even be crucial to upcoming quantum computing innovations.
According to Philip Moll, director of the German Max Planck Institute for the Structure and Dynamics of Matter, "this paper shows that the superconducting diode is an entirely solved problem from an engineering perspective." Moll did not participate in the project. The genius of this work is that [Moodera and colleagues] got record efficiency without even trying, and their structures are still far from being optimised.
According to Jagadeesh Moodera, senior research scientist and project leader at MIT's Department of Physics, "our engineering of a superconducting diode effect that is robust and can operate over a wide temperature range in simple systems and potentially opening the door for novel technologies." Moodera is also connected to the Plasma Science and Fusion Centre (PSFC), the Francis Bitter Magnet Laboratory, and the Materials Research Laboratory.
Scaling up is simple for the nanoscopic rectangular diode, which is around 1,000 times smaller in diameter than a human hair. On a single silicon wafer, millions may be manufactured.
Diodes are a common component in computer systems because they make it easy for electricity to flow in one direction but not the other. The transistors found in today's semiconductor computer chips number in the billions. The high-power systems in the data centres that support a wide range of contemporary technologies, including cloud computing, must be cooled using enormous quantities of energy since these devices can become quite hot owing to electrical resistance. In ten years, these systems might consume up to 20% of the world's energy, according to a 2018 Nature news article.
The development of superconducting diodes has therefore become a hot issue in condensed matter physics. This is because superconductors are significantly more efficient than their semiconducting counterparts, which exhibit observable energy loss in the form of heat, in that they transfer current with zero resistance below a specific low temperature (the critical temperature).
However, prior solutions to the issue have required significantly more intricate physics. "The impact we identified is due [in part] to a ubiquitous superconductor feature that can be produced in a very plain, easy way. Moodera explains, "It simply stares you in the face.
"The work is an important counterpoint to the current fashion to associate superconducting diodes with exotic physics, such as finite-momentum pairing states," explains Moll of the Max Planck Institute for the Structure and Dynamics of Matter. As a result of some violated symmetries, a superconducting diode is really a common and pervasive phenomena occurring in classical materials.
In 2020, Majorana fermions, an unusual particle pair, were discovered by Moodera and his colleagues. These particle pairings could result in the development of a new family of topological qubits, the fundamental units of quantum computing. The team came to the conclusion that the material platform they developed for the Majorana work might also be used to solve the challenge of making superconducting diodes as they considered various methods.
They had it right. They created multiple versions of superconducting diodes using that same framework, each one being more effective than the last. The first, for instance, was made of a superconducting layer of vanadium that was designed into a common component of electronics (the Hall bar). They observed the diode effect—a huge polarity dependency for current flow—when they introduced only a small magnetic field corresponding to the magnetic field of the Earth.
They next made another diode by stacking a superconductor with a ferromagnet—in this case, a ferromagnetic insulator—a substance that generates a small magnetic field of its own. They discovered a larger diode effect that remained stable even after the initial magnetic field was switched off after adding a minor magnetic field to the ferromagnet in order to magnetise it so that it creates its own field.
The crew continued to investigate the situation.
Superconductors are recognised for their ability to carry electricity without resistance, but they also possess other less well-known unique characteristics. They repel magnetic fields, for instance, on approach. Superconductors create an internal supercurrent when they are subjected to a weak magnetic field. This internal supercurrent causes its own magnetic flux, which cancels the external field, preserving the superconducting state. The Meissner screening effect may be compared to the immune system of our bodies producing antibodies to combat bacterial and other disease infections. However, there is a limit to how well this works. Similar to magnetic fields, superconductors are not completely immune to them.
The team's developed diodes take use of this common Meissner screening phenomenon. The minuscule magnetic field they applied triggers the material's screening current mechanism, which expels the external magnetic field and preserves superconductivity. They could have delivered the field directly or through the nearby ferromagnetic layer.
The scientists also discovered that minute variations between the two sides or edges of the diode devices are a crucial component in optimising these superconductor diodes. According to Moodera, these variations "create some sort of asymmetry in the magnetic field entry into the superconductor."
The researchers discovered that they might boost efficiency from 20% to more than 50% by designing their own type of diode edges to optimise these differences—for instance, one edge has sawtooth characteristics while the other edge is left unaltered. According to Moodera, this finding makes it possible for devices to have edges that can be "tuned" for even greater efficiency.
The scientists concluded that the diode effect was a combined result of the edge asymmetries inside superconducting diodes, the universal Meissner screening effect observed in all superconductors, and a third feature of superconductors known as vortex pinning.
Yasen Hou, the paper's first author and a postdoctoral associate at the Francis Bitter Magnet Laboratory and the PSFC, says "It is fascinating to see how inconspicuous yet ubiquitous factors can create a significant effect in observing the diode effect. What's more intriguing is that [this work] offers a simple strategy with enormous potential to boost productivity."
In Germany, the University of Regensburg's professor Christoph Strunk , who was not engaged in the study, says "demonstrates that the supercurrent in simple superconducting strips can become non-reciprocal. Even in the absence of an external magnetic field, the diode effect may be maintained when used in conjunction with a ferromagnetic insulator. The remanent magnetization of the magnetic layer may be used to programme the direction of rectification, which may have many uses in the future. Both from the perspective of fundamental research and practical applications, the work is significant and intriguing."
The two researchers who developed the modified edges, according to Moodera, did it over the course of a summer in his lab when they were still in high school. They are Amith Varambally of Vestavia Hills, Alabama, who will enrol at the California Institute of Technology, and Ourania Glezakou-Elbert of Richland, Washington, who will attend Princeton this September.
"I didn't know what to expect when I set foot in Boston last summer, and I definitely never expected to [be] a coauthor in a Physical Review Letters paper," says Varambally.
Every day was interesting, whether I was reading plenty of articles to learn more about the diode phenomenon, running equipment to create new diodes for research, or talking to Ourania, Dr. Hou, and Dr. Moodera about our work.
I'm really thankful to Drs. Moodera and Hou for giving me the chance to work on such an interesting topic, as well as to Ourania for being a fantastic research collaborator and friend.
Reference: “Ubiquitous Superconducting Diode Effect in Superconductor Thin Films” by Yasen Hou, Fabrizio Nichele, Hang Chi, Alessandro Lodesani, Yingying Wu, Markus F. Ritter, Daniel Z. Haxell, Margarita Davydova, Stefan Ilić, Ourania Glezakou-Elbert, Amith Varambally, F. Sebastian Bergeret, Akashdeep Kamra, Liang Fu, Patrick A. Lee and Jagadeesh S. Moodera, 13 July 2023, Physical Review Letters.
DOI: 10.1103/PhysRevLett.131.027001
In addition to Moodera and Hou, corresponding authors of the paper are Professors Patrick A. Lee of MIT Physics and Akashdeep Kamra of Universidad Autónoma de Madrid. Other authors from MIT are Liang Fu and Margarita Davydova of MIT Physics, and Hang Chi, Alessandro Lodesani, and Yingying Wu, all of the Francis Bitter Magnet Laboratory and the Plasma Science and Fusion Center. Chi is also affiliated with the U.S. Army CCDC Research Laboratory.
Authors also include Fabrizio Nichele, Markus F. Ritter, and Daniel Z. Haxwell of IBM Research Europe; Stefan Ilićof Centro de Física de Materiales (CFM-MPC); and F. Sebastian Bergeret of CFM-MPC and Donostia International Physics Center.
This work was supported by the Air Force Office of Sponsored Research, the Office of Naval Research, the National Science Foundation, and the Army Research Office. Additional funders are the European Research Council, the European Union’s Horizon 2020 Research and Innovation Framework Programme, the Spanish Ministerio de Ciencia e Innovacion, the A. v. Humboldt Foundation, and the Department of Energy’s Office of Basic Sciences.