Layer graphene superconductivity is surprisingly strange

Why do thin cold carbon sheets offer resistance to electric currents? Two experiments are bringing us closer to an answer, and perhaps even practical ambient superconductors.

Kin Chung Fong At Northeastern University in Massachusetts, it was surprised when another physique, Abhishek Banerjee At Harvard University, he told him a number during dinner. They were studying different aspects of graphene, carbon sheets of a thick atom, but both made the same estimate about how difficult it should be for an electric current that flows through graphene to change suddenly.

Past experiments have shown that very cold batteries of two or three layers of graphene can perfectly superconduct or perform electricity without resistance and loss of energy, if some of the sheets are rotated by a special angle. But why this happens was still mysterious. The two physicists thought that the property they estimated at dinner, called kinetic inductance, could illuminate the answer.

“The feeling was like when you are in a wooden hiking [through] The forest, and suddenly you find, well, wait a minute, I am not the only person in this deep forest, “says Fong.

Together with other colleagues, they turned their idea into two experiments. A group measured kinetic inductance for two layers of stacked and crooked graphene; A second group focused on three layers.

Joel Wang In the Massachusetts Institute of Technology, which was in the group that worked in two -layer graphene, says that measuring kinetic inductance had been previously difficult. Because multilayer graphene can only occur in very small pieces, standard techniques to measure their superconductive currents, such as exposing it to magnetic particles or fields, produced excessively weak signals. On the other hand, both teams had to innovate a configuration where small graphene flakes were exposed to microwave, while researchers slowly varied properties such as temperature, which must be maintained very low so that superconductivity occurs at all.

We know that multicapa graphene superconducts because electrons inside them are combined, and these pairs flow in currents more easily than individual particles. But electrons generally repel each other. How the particles are united exactly and what properties these peers have yet understood.

“The theory is [running] Behind the experiments here, ”he says Miuko Tanaka at the University of Tokyo, which was also in the two -layer group.

For two layers of graphene, his team discovered that the superconductive current is much “more rigid”, resists the change more, than predicts any conventional theory of superconductivity. They traced this anomaly called quantum geometry. Specifically, the shape of the wave functions of electrons, which encode all their properties and possible behaviors, seemed to boost this exotic type of superconductivity.

In Triayer’s graphene, researchers found surprising similarities between the kinetic inductance of their sample and the behavior of a family of completely different superconductors, which maintain their special properties at much higher temperatures.

Because of this, both Banerjee and Tanaka say that these experiments can make more than shed light on why graphene superconducts could also reveal the necessary key properties for room temperature superconductors. Physicists have been looking for such materials for decades in the hope that using them can radically reduce the energy consumption of many devices.

“We are finding interesting laws that seem to arise in both material systems. Maybe what we are discovering is something deeper, ”says Banerjee. Both teams plan to perform similar experiments with other very thin superconductors.

“Recently, there have been so many new two -dimensional superconductors that are interesting, surprising and a bit unusual,” he says Zeyu haoAlso at Harvard University, which was in the team investigating three -layer graphene. For example, earlier this month, a different team published an investigation that shows that two -layer crystals of a material called tungsten deselenide exhibit superconductivity when the layers twist in relation to each other.

Meanwhile, the colleague of Hao Mary KreidelNow in the NASA Jet Propulsion Laboratory in California, it already has an application in mind for stacked and crooked graphene. She is working on particle detectors for space missions, many of which use superconductors. They could become smaller and lighter, a crucial advantage on the space flight, if they were made of multicapa graphene, she says.