New material could be two superconductors in one | MIT news


MIT physicists and colleagues have demonstrated an exotic form of superconductivity in a new material that the team only synthesized about a year ago. Although predicted in the 1960s, this type of superconductivity has so far proven difficult to stabilize. In addition, the scientists found that the same material could possibly be manipulated to exhibit another, equally exotic form of superconductivity.

The work was reported in the November 3rd issue of the journal nature.

The demonstration of finite momentum superconductivity in a layered crystal known as a natural superlattice means that the material can be optimized to create different superconductivity patterns within the same sample. And that, in turn, could have implications for quantum computing and more.

The material is also intended to become an important tool for uncovering the secrets of unconventional superconductors. This can be useful for new quantum technologies. Developing such technologies is challenging, in part because the materials they are made of can be difficult to study. The new material could simplify such research because, among other things, it is relatively easy to manufacture.

“An important topic in our research is that new physics emerge from new materials,” says Joseph Checkelsky, senior researcher at the work and Mitsui Career Development Associate Professor of Physics. “Our first report last year looked at this new material. This new work reports on the new physics. “

Checkelsky’s co-authors on the current work include lead author Aravind Devarakonda PhD ’21, now at Columbia University. The work was a central part of Devarakonda’s thesis. Co-authors are Takehito Suzuki, a former researcher at MIT, now at Toho University in Japan; Shiang Fang, postdoctoral fellow at MIT’s Department of Physics; Junbo Zhu, physics student at MIT; David Graf of the National High Magnetic Field Laboratory; Markus Kriener from the RIKEN Center for Emergent Matter Science in Japan; Liang Fu, associate professor of physics at MIT; and Efthimios Kaxiras from Harvard University.

New quantum material

Classical physics can be used to explain a wide variety of phenomena that underlie our world – until things get exquisitely small. Subatomic particles like electrons and quarks behave differently in ways that are not yet fully understood. Enter quantum mechanics, the field that tries to explain its behavior and the resulting effects.

Checkelsky and colleagues discovered a new quantum material, or one that manifests the exotic properties of quantum mechanics on a macroscopic scale. In this case it is a superconductor.

Checkelsky explains that the realization of special superconductors that are two-dimensional or only a few atomic layers thick has recently experienced a boom. One of the reasons why these new ultra-thin superconductors are interesting is that they are expected to provide insights into superconductivity itself.

But there are challenges. On the one hand, materials that are only a few atomic layers thick are difficult to examine themselves because they are so sensitive. Could there be another approach to unravel its secrets?

Checkelsky and colleagues’ new material can be thought of as the superconducting equivalent of a layered cake, where one layer is an ultra-thin film of superconducting material while the next is an ultra-thin spacer layer that protects it. Stacking these layers on top of one another results in a large crystal (this occurs naturally when the constituents sulfur, niobium, and barium are heated together). “And this macroscopic crystal that I can hold in my hand behaves like a 2D superconductor. It was very surprising, ”says Checkelsky.

Many of the probes that scientists use to study 2D superconductors are difficult to use on atomically thin materials. Because the new material is so big, “we now have a lot more tools” [to characterize it]“Says Checkelsky. In fact, for the work reported in the current paper, the scientists used a technique that requires massive samples.

Exotic superconductors

A superconductor carries a charge in a special way. Instead of an electron, the charge is carried by two electrons that are connected to one another in what is known as a Cooper pair. However, not all superconductors are created equal. Some unusual forms of superconductivity can only occur if the Cooper pairs can move freely through the material over relatively long distances. The longer the distance, the “cleaner” the material.

The Checkelsky team’s material is extremely clean. As a result, physicists were curious to see if what it does could be in an unusual superconducting state. In the current work, the team shows that their new material is a finite impulse superconductor when a magnetic field is applied. This particular type of superconductivity, which was proposed in the 1960s, has remained a fascination for scientists to this day.

While superconductivity is usually destroyed by modest magnetic fields, a finite momentum superconductor can persist by forming a regular pattern of regions with many Cooper pairs and regions that have none. It found that this type of superconductor can be manipulated to form a variety of unusual patterns when Cooper pairs move between quantum mechanical orbits known as Landau levels. And that means, according to Checkelsky, that scientists should now be able to create different patterns of superconductivity within the same material.

“This is an impressive experiment capable of demonstrating Cooper pairs moving between Landau levels in a superconductor, something that has never been observed before. In all honesty, I never expected to see this in a crystal that you could be holding in your hand so this is very exciting. In order to observe this elusive effect, the authors had to carry out meticulous and highly precise measurements on a previously discovered unique two-dimensional superconductor. It’s a remarkable feat, not just in terms of its technical difficulty, but also its cleverness, ”said Kyle Shen, professor of physics at Cornell University. Shen was not involved in the study.

The physicists also recognized that their material also contains the ingredients for another exotic type of superconductivity. Topological superconductivity involves the movement of charge along edges or boundaries. In this case this charge could migrate along the edges of any internal superconducting pattern.

Checkelsky’s team is currently working to see whether their material is actually capable of topological superconductivity. If so, “can we combine both new types of superconductivity? What good could that do? ”Checkelsky asks.

“It was a lot of fun creating this new material,” he concludes. “When we looked carefully at what it could do, there were a number of surprises. It’s really exciting when new things come out that we didn’t expect. “

This work was supported by the Gordon and Betty Moore Foundation, the Office of Naval Research, the Office of Science of the US Department of Energy (DOE), the National Science Foundation (NSF), and the Rutgers Center for Materials Theory.

The calculations were carried out at Harvard University. Other parts of the work were done at the National High Magnetic Field Laboratory, which is supported by the NSF, the State of Florida, and the Department of Energy.

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