Novel technique for tuning superconductivity levels

Researchers have discovered evidence that superconductivity can be controlled by influencing the surrounding environment, a finding that may lead to more efficient electronics down the road, according to a new study.

Superconductivity, or the ability of certain materials to conduct electric currents without any energy loss when cooled below a critical temperature, is a property still not very well understood. While a major challenge, understanding more about its formation mechanisms could lead to better, longer-lasting materials as well as more powerful quantum devices.

Led by Chun Ning (Jeanie) Lau, senior author of the study and a professor of physics at The Ohio State University, the research team constructed a special material called twisted bilayer graphene — a layer of carbon stacked onto another and rotated at a small angle.

By attaching the material to a man-made synthetic diamond called strontium titanate, Lau and colleagues were able to see and control how strongly electrons — tiny subatomic particles — in the system interacted with each other. Electron interactions that control properties like magnetic states and chemical bonding come in pairs, and by adjusting the ‘settings’ of these pairs, the team was able to switch the material’s superconductivity on and off.

“Electrons normally repel each other, but in superconductors they form pairs; this pair formation is the key to a superconductor’s ability to conduct electricity without dissipation,” Lau said. “Our evidence suggests that electrons themselves, depending on their sensitivity to their nearby environment, are unexpectedly important for material changes.”

The researchers were surprised to find that when they increased their adjustments, superconductivity had decreased. This result is different from conventional superconductors, where, if repelling forces between electrons are suppressed, the pairing gets stronger, highlighting the unusual nature of new materials like twisted bilayer graphene to successfully direct electricity.

“If you could transmit electricity without energy loss, that would be hugely important for technologies used in our everyday life,” Lau said. “Despite the fundamental questions that still need answers, this work basically provides a path toward a new type of physics mechanism.”

Such a discovery could help scientists develop materials that superconduct at higher temperatures — even room temperature, a ‘holy grail’ in the field that, if achieved, could transform their current understanding of electronics, power transmission and communications.

The study was published in the journal Nature Physics.

Overall, these results reveal a simpler way to control the conditions needed to create and control the atomic power behind superconductivity. For instance, because many high-temperature superconductors have limitations that cap their productivity, using the environment to drive their abilities could boost their power as well as allow scientists to build more efficient electronics.

These potential applications are not far off, according to Xueshi Gao, lead author of the study and a current PhD student in physics at Ohio State: he believes his team’s findings will soon be useful to many different types of systems and experiments across the field.

“The mechanism of superconductivity in the twisted bilayer graphene system we used is still not well understood,” Gao said. “But our result can shed light on and help people to better understand the concept when applying it to future work.”

Still, the team emphasises that the model is only an initial step towards understanding unexplored electronic interactions, and next steps will involve testing other types of interactions and investigating the various complex physics questions that their work opens up.

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