Scientists from The University of Texas at Dallas and The Ohio State University have discovered a way for materials to become superconductors even when the electrons are barely moving. This discovery could help with the development of new superconductors.
Scientists recently published their study findings in the journal Nature which showed a way to measure the speed of electrons. This is the first time that quantum geometry has been identified as the major factor behind superconductivity in any material.
Researchers studied something called twisted bilayer graphene. It’s made up of two layers of carbon atoms arranged like honeycombs placed side by side at a slight angle to each other. When this special angle is just right, it causes the electrons in the material to move very slowly. That’s what scientists call a “magic twist angle”. The study on this was written by Dr. Fan Zhang from UT Dallas who already wrote a review article about the unique properties found in these systems.
In most metals, the electrons move quickly and that’s what makes them conduct electricity. Superconductors are different because their electrons join together in pairs to flow without any resistance or energy loss. However, when it comes to twisted bilayer graphene, its electrons move incredibly slowly – almost like they’ve stopped moving altogether! It’s really confusing how these slow electrons can still allow an electrical current to pass through it and even make superconductivity possible.
Researchers have found that superconductivity, which is a process when materials allow electrons to flow without resistance, doesn’t come from anything as simple as electrical charge; instead it happens because of tiny changes in the material’s shape on an atomic level. This new understanding has opened up new ways to make materials with very low resistance and could help us create better technology.
Researchers from Ohio State, led by Dr. Marc Bockrath, Dr. Jeanie Lau and Dr. Mohit Randeria created a graphene device to find the speed of electrons in it. This type of physics is called condensed matter physics and they used something called the Schwinger effect which makes electron-positron pairs when an electric field is present. This was the first time that this particular Schwinger effect, which was predicted but not proven before, was seen in any superconductor.
Tianyi Xu, a student in Zhang’s Physics theory group and one of the authors of the article said that they found out that the speed is the slowest so far among all graphene systems. Superconductivity can still appear however, even though it is surprising. They needed to figure out how to measure electron velocity as this was an important step for calculating the contribution of superconductivity. The result is that the contribution of superconductivity is very tiny.
The scientists did experiments and calculations to show that the main cause of superconductivity is actually something called quantum geometry. This is like ordinary geometry, but it’s based on things from quantum physics.
Patrick Cheung MS’22 PhD’22, a former student of Zhang and author of the article, said that like a balloon in our three-dimensional space, all its properties can be explained using measurements and curves on its surface. This is true for the area where quantum electrons live as well. It’s called the Hilbert Space and it gives rise to interesting materials and applications such as superconductivity and intelligent quantum sensing, which they had also studied before.
Researchers have recently discovered a special type of superconductor that works with quantum geometry. This could help create new kinds of superconductors that work at temperatures higher than today’s ones, which usually only work when it’s really cold (-123 degrees Celsius or -190 Fahrenheit).
Xu said that it would be incredible if scientists could create a material which could work at room temperature and allow electricity to flow without losing any of its power. This material would make things such as maglev trains much less costly.
Zhang added that there is still a lot of really cool physics to discover using quantum geometry.
This research was conducted by scientists from Ohio State University as well as the National Institute for Materials Science in Japan. The findings were published on 15 February 2023 in a journal named “Nature”: https://www.nature.com/articles/s41535-021-00410-w
The money for the UTD scientists doing this work was given by the National Science Foundation and the Army Research Office, which is a part of the United States Army.
