MIT scientists and their colleagues have created a simple superconducting device that can transmit electrical current through electronic devices more efficiently than today. As a result, new diodes (a type of switch) can drastically reduce the energy consumption of high-power computing systems, a major problem that is expected to become more severe. Although the diode is in the early stages of development, it is more than twice as efficient as similar diodes reported by others. It may even become an integral part of emerging quantum computing technology.
The work was published in the online journal on July 13 Physical Review Lettersalso the subject of news reports journal of physics.
“This paper shows that from an engineering perspective, superconducting diodes are a completely solved problem,” said Philip Moll, director of the Max Planck Institute for the Structure and Dynamics of Matter in Germany. Moll Not involved in this work. “beautiful [this] work is [Moodera and colleagues] Get record-breaking efficiency without trying [and] Their structure is far from optimized. “
“The superconducting diode effect we designed is so powerful that it can operate over a wide range of temperatures in a simple system, potentially opening the door to new technologies,” said the leader of the current work, a senior in MIT’s Department of Physics. said research scientist Jagadeesh Moodera. physics. Moodera is also affiliated with the Materials Research Laboratory, the Francis Butte Magnet Laboratory and the Plasma Science and Fusion Center (PSFC).
The nanoscale rectangular diodes – about 1,000 times thinner than the diameter of a human hair – are easily scalable. Millions of wafers can be produced on a single wafer.
Towards superconducting switches
A diode, a device that allows electricity to flow easily in one direction but not the other way around, is ubiquitous in computing systems. Modern semiconductor computer chips contain billions of diode-like devices called transistors. However, these devices can become very hot due to electrical resistance, requiring large amounts of energy to cool the high-power systems in data centers behind many modern technologies such as cloud computing.According to a 2018 news feature naturethese systems could use nearly 20% of the world’s electricity within 10 years.
Therefore, making diodes made of superconductors has been a hot topic in condensed matter physics. This is because superconductors carry current completely without resistance below a certain low temperature (critical temperature) and are therefore more efficient than their semiconductor counterparts, which lose significant energy in the form of heat.
However, other approaches to this problem so far have involved more complex physics. “The effect we found was due to [in part] The universal properties of superconductors can be achieved in a very simple and straightforward way. It just stares you in the face,” Mudra said.
Mohr from the Max Planck Institute said: “This work is an important rebuttal to the current popularity of superconducting diodes. [with] Strange physics, such as finite momentum paired states. In fact, due to certain symmetry breaking, superconducting diodes are a common and widespread phenomenon in classical materials. “
A somewhat accidental discovery
In 2020, Mudra and colleagues observed evidence of pairs of exotic particles known as Majorana fermions. These particle pairs could give rise to a new family of topological qubits, the building blocks of quantum computers. While thinking about ways to make superconducting diodes, the team realized that the materials platform they developed for Majorana’s work might also be applicable to the diode problem.
They are right. Using this common platform, they developed different versions of superconducting diodes, each more efficient than the last. For example, the first material consists of nanoscale thin layers of vanadium, a superconductor, patterned into structures common in electronic devices (Hall rods). When they applied a tiny magnetic field comparable to the Earth’s magnetic field, they saw a diode effect – a huge polarity dependence of the electrical current.
They then created another diode, this time layering the superconductor with a ferromagnet (in their case, a ferromagnetic insulator), a material capable of generating its own tiny magnetic field. After applying a tiny magnetic field to magnetize a ferromagnet so that it generates its own magnetic field, they found a larger diode effect that remained stable even after the original magnetic field was turned off.
ubiquitous properties
The team continues to figure out what’s going on.
In addition to transmitting electrical current without resistance, superconductors have other, less well-known but equally common properties. For example, they don’t like magnetic fields getting inside. When exposed to a tiny magnetic field, a superconductor generates an internal supercurrent that induces its own magnetic flux and cancels out the external magnetic field, thereby maintaining its superconducting state. This phenomenon is known as the Meissner screening effect and can be thought of as analogous to our body’s immune system releasing antibodies to fight infections from bacteria and other pathogens. However, this only works within certain limits. Likewise, superconductors cannot completely block large magnetic fields.
The diode the team created takes advantage of this universal Meissner shielding effect. The tiny magnetic fields they applied directly or through adjacent ferromagnetic layers activated the material’s shielding current mechanism to expel external magnetic fields and maintain superconductivity.
The team also discovered that another key factor in optimizing these superconducting diodes is the small differences between the sides, or edges, of the diode device. These differences “create a certain asymmetry in the way the magnetic field enters the superconductor,” Mudra said.
By designing their own edge forms on the diodes to optimize these differences (for example, one edge had jagged features while the other was not intentionally altered), the team found they could increase efficiency from 20 percent to more than 50 percent. Mudra said the discovery opens the door for devices whose edges could be “tuned” for greater efficiency.
In summary, the team discovered that edge asymmetries within superconducting diodes, the Meissner shielding effect prevalent in all superconductors, and a third property of superconductors called vortex pinning combine to produce the diode effect.
“It’s fascinating to see how humble but ubiquitous factors can have a dramatic impact on observing diode effects,” said the paper’s first author Yasen Hou, a postdoc in Francis Bitter Magnet’s laboratory and PSFC. “It’s even more fascinating. Excited [this work] A simple approach is provided with great potential for further efficiency improvements. “
Christoph Strunk is a professor at the University of Regensburg, Germany. “The current work shows that supercurrents in simple superconducting strips may become irreversible,” said Strunk, who was not involved in the study. Furthermore, when combined with a ferromagnetic insulator, it can even occur in the absence of an external magnetic field. down holding diode effect. The rectification direction can be programmed by the residual magnetization of the magnetic layer, which may have great potential in future applications. This work is important and Attractive.”
Teen Contributors
Mudra noted that the two researchers who created Engineering Edge completed the work during a summer in Mudra’s lab while still in high school. They are Ourania Glezakou-Elbert from Richland, Wash., who will attend Princeton University this fall, and Vestavia Hills, Ala. Amith Varambaly, who will attend Caltech.
“When I stepped foot in Boston last summer, I had no idea what to expect and certainly never imagined what would happen,” Varambally said. [be] co-author Physical Review Letters Paper.
“Every day is exciting, whether it’s reading dozens of papers to better understand diode phenomena, operating machines to make new diodes for research, or discussing our research with Ourania, Dr. Hou, and Dr. Moodera.
“I am extremely grateful to Dr. Moodera and Dr. Hou for providing me with the opportunity to work on such a fascinating project, and to Ourania for being a great research partner and friend.”
In addition to Moodera and Hou, the corresponding authors of the paper are Professor Patrick A. Lee of the MIT Department of Physics and Professor Akashdeep Kamra of the Autonomous University of Madrid. Other MIT authors include Liang Fu and Margarita Davydova of the Department of Physics, and Hang Chi, Alessandro Lodesani, and Yingying Wu of the Francis Bitter Magnet Laboratory and Center for Plasma Science and Fusion. 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 Illich Center for Materials Physics (CFM-MPC); and F. Sebastian Bergeret of CFM-MPC and International Physics Center Donostia.
This work was supported by the Air Force Research Office, Office of Naval Research, National Science Foundation, and Army Research Office. Other funders include the European Research Council, the European Union’s Horizon 2020 research and innovation framework program, the Spanish Ministry of Science and Innovation, the A. v. Humboldt Foundation and the Office of Basic Sciences of the Department of Energy.