Amazing Discovery of a Unidirectional Superconductor – Thought Impossible

An artistic impression of a superconducting chip. Credit: TU Delft

Associate Professor Mazhar Ali and his research group at Delft University of Technology (TU Delft) have discovered unidirectional superconductivity without magnetic fields, something that has been thought impossible since its discovery in 1911 – until now. The discovery published in the journal temper nature, It takes advantage of 2D quantum materials and paves the way toward superconducting computing. Superconductors can make electronics hundreds of times faster, all without a loss of power.

Ali: 20y Century was the semiconductor century, 21St It could become the horn of the superconductor.”

Throughout the 20th century, many scientists, including Nobel Prize laureates, struggled over the nature of superconductivity, which was discovered by Dutch physicist Kamerling Onnes in 1911. In superconductors, current flows through a wire without resistance, which means that it is difficult to dampen this current Or even block it—not to mention making current flow only in one direction without the other. The fact that Ali’s group was able to make a unidirectional superconductor—something required for computing—is remarkable: It’s like inventing a special kind of ice that has no friction in one way but insurmountable friction in the other.

Superconductor: Ultrafast, Ultragreen

The advantages of applying superconductors to electronics are twofold. Superconductors can make electronics hundreds of times faster, and incorporating superconductors into our daily lives will make IT more environmentally friendly: if you spin a superconducting wire from here to the moon, it will transmit power without any loss. For example, the use of superconductors instead of ordinary semiconductors could provide up to 10% of all Western energy reserves according to the NWO.

According to the Dutch Research Council (NWO), the use of superconductors instead of conventional semiconductors could provide up to 10% of all Western energy reserves.

Super Connectivity Applicability

in 20y A century and beyond, no one could contend with the barrier of making superconducting electrons only go in one direction, a fundamental property necessary for computing and other modern electronics (consider for example diodes that go in one direction as well). In normal conduction, electrons fly as separate particles; In superconductors they move in pairs of two, without any loss of electrical energy. In the 1970s, scientists at IBM experimented with the idea of ​​superconducting computing but had to give up their efforts: in their papers on the topic, IBM stated that without non-reciprocal superconductivity, running a computer on superconductors would be impossible.

superconductivity It is a set of physical properties that appear in some materials in which electrical resistance disappears and magnetic flux fields are expelled. A superconductor is any material that possesses these qualities.

An interview with the writer Mazhar Ali

Q: Why, when unidirectional work with normal semiconductivity, did superconductivity not work in one direction before?

Mazhar Ali: “The electrical conductivity in a semiconductor, such as Si, can be in one direction due to a constant internal electric dipole, and therefore there can be a network based on its potential. The textbook example is the famous “pn junction”; where we combine two of semiconductors: one has extra electrons (-) and one has extra (+) holes.The charge separation makes a net, latent intrinsic feel of the electron flying through the system.This breaks symmetry and can result in ‘one-way’ properties because the forward And the back, for example, are no longer the same. There is a difference in going in the same direction as the dipole versus the opposite direction to it; similar to if you were swimming with a river or swimming in a river.”

“Superconductors have no equivalent to this one-way idea without a magnetic field because they are more bound to metals (i.e. conductors, as the name says) than to semiconductors, which always run in both directions and have no combined potentials. Likewise, Josephson junctions (JJs) ), which are sandwiches of two superconductors with traditional non-superconducting insulating materials between superconductors, also did not have any particular symmetry-breaking mechanism that led to a difference between “forward” and “backward.”

Q: How did you manage to do what seemed impossible at first?

Ali: “It was really the result of one of my group’s fundamental research directions. In what we call ‘quantum Josephson junctions’ (QMJJs), we replace the classic barrier material in JJs with a quantum material barrier, in which the intrinsic properties of quantum material can modulate the coupling between two superconductors in new ways. Josephson Diode was an example: we used the quantum material Nb3u8which is a two-dimensional material like[{” attribute=””>graphene that has been theorized to host a net electric dipole, as our quantum material barrier of choice and placed it between two superconductors.”

“We were able to peel off just a couple atomic layers of this Nb3Br8 and make a very, very thin sandwich — just a few atomic layers thick — which was needed for making the Josephson diode, and was not possible with normal 3D materials. Nb3Br8, is part of a group of new quantum materials being developed by our collaborators, Professor Tyrel McQueen’s and his group at Johns Hopkins University in the USA, and was a key piece in us realizing the Josephson diode for the first time.”

Q: What does this discovery mean in terms of impact and applications?

Ali: “Many technologies are based on old versions of JJ superconductors, for example, MRI technology. Also, quantum computing today is based on Josephson Junctions. Technology that was previously only possible using semiconductors can now potentially be made with superconductors using this building block. This includes faster computers, as in computers with up to terahertz speed, which is 300 to 400 times faster than the computers we are now using. This will influence all sorts of societal and technological applications. If the 20th century was the century of semiconductors, the 21st can become the century of the superconductor.”

“The first research direction we have to tackle for commercial application is raising the operating temperature. Here we used a very simple superconductor that limited the operating temperature. Now we want to work with the known so-called “High Tc Superconductors”, and see whether we can operate Josephson diodes at temperatures above 77 K, since this will allow for liquid nitrogen cooling. The second thing to tackle is scaling of production. While it’s great that we proved this works in nanodevices, we only made a handful. The next step will be to investigate how to scale production to millions of Josephson diodes on a chip.”

Q: How sure are you of your case?

Ali: “There are several steps which all scientists need to take to maintain scientific rigor. The first is to make sure their results are repeatable. In this case we made many devices, from scratch, with different batches of materials, and found the same properties every time, even when measured on different machines in different countries by different people. This told us that the Josephson diode result was coming from our combination of materials and not some spurious result of dirt, geometry, machine or user error or interpretation.”

“We also carried out “smoking gun” experiments that dramatically narrows the possibility for interpretation. In this case, to be sure that we had a superconducting diode effect we actually tried “switching” the diode; as in we applied the same magnitude of current in both forward and reverse directions and showed that we actually measured no resistance (superconductivity) in one direction and real resistance (normal conductivity) in the other direction.”

“We also measured this effect while applying magnetic fields of different magnitudes and showed that the effect was clearly present at 0 applied field and gets killed by an applied field. This is also a smoking gun for our claim of having a superconducting diode effect at zero-applied field, a very important point for technological applications. This is because magnetic fields at the nanometer scale are very difficult to control and limit, so for practical applications, it is generally desired to operate without requiring local magnetic fields.”

Q: Is it realistic for ordinary computers (or even the supercomputers of KNMI and IBM) to make use of superconducting?

Ali: “Yes it is! Not for people at home, but for server farms or for supercomputers, it would be smart to implement this. Centralized computation is really how the world works now-a-days. Any and all intensive computation is done at centralized facilities where localization adds huge benefits in terms of power management, heat management, etc. The existing infrastructure could be adapted without too much cost to work with Josephson diode based electronics. There is a very real chance, if the challenges discussed in the other question are overcome, that this will revolutionize centralized and supercomputing!”

On May 18th – 19th, Professor Mazhar Ali and his collaborators Prof. Valla Fatemi (Cornell University) and Dr. Heng Wu (TU Delft) are hosting a “Superconducting Diode Effects Workshop” on the Virtual Science Forum, in which 12 international experts in the field will be giving recorded talks online (to be published on YouTube) about the current state of the field as well as future research and development directions.

Reference: “The field-free Josephson diode in a van der Waals heterostructure” 27 April 2022, Nature.
DOI: 10.1038/s41586-022-04504-8

Associate professor Mazhar Ali studied at UC Berkeley and Princeton and did his postdoc at IBM and won the Sofia Kovalevskaja Award from the Alexander von Humboldt Foundation in Germany before joining the faculty of Applied Sciences in Delft.

Leave a Reply

%d bloggers like this: