For the first time, scientists are watching 2D plots of electrons spontaneously emerge in a 3D superconducting material.

Creating a two-dimensional material, only a few atoms thick, is often a difficult process that requires advanced equipment. Scientists were therefore surprised to see 2D splashes emerge in a three-dimensional superconductor – a material that moves electrons with 100% efficiency and zero resistance – without cause.

Within the splashes, superconducting electrons acted as if they were in an incredibly thin, skin-like plane, a situation that required them to somehow transition to another dimension, where different rules of quantum physics apply.

“This is a tantalizing example of emerging behavior, which is often difficult or impossible to repeat by trying to construct it in advance,” said Hari Manoharan, a professor at Stanford University and researcher at the Stanford Institute for Materials and Energy. Sciences (SIMES), said. at the SLAC National Accelerator Laboratory of the Department of Energy, which led the research.

“It’s as if the power is given to conduct super,” he said, “the 3D electrons themselves choose to live in a 2D world.”

The research team calls this new phenomenon “inter-dimensional superconductivity”, and in a report in the Proceedings of the National Academy of Sciences today they suggest that this is how 3D superconductors reorganize themselves just before undergoing a sudden shift to an insulating state, where electrons are confined to their atoms and cannot move at all.

“What we found was a system where electrons behave in unexpected ways. That’s the beauty of physics,” said Carolina Parra, a postdoctoral researcher at SLAC and Stanford, when conducting the experiments that led to the visualization. hereof. intriguing result. “We were very lucky to find this behavior.”

Electrons that act strangely

Although superconductivity was discovered more than a century ago, its usefulness is limited by the fact that materials have only become conductive at temperatures close to those in deep space.

The announcement in 1986 that scientists had discovered a new and unexpected class of superconducting materials that were much higher – though still very cold – set in motion a tsunami that continues to this day, with the aim of finding out how the new material uses and develops versions that work closer to room temperature for applications such as perfectly efficient power lines and maglev trains.

This study started with a high temperature superconductor called BPBO for its four atomic constituents – barium, lead, bismuth and oxygen. It was synthesized in the laboratory of Stanford Professor and SIMES researcher Ian Fisher by Paula Giraldo-Gallo, a doctor. then student.

As researchers did routine tests there, including determining the transition temperature at which it flips between a superconducting and an insulating phase – such as water that turns into steam or ice – they realized that their data showed that electrons acted as if they were up to ultradun limited, 2D layers or stripes within the material. This was a mystery because BPBO is a 3D superconductor whose electrons are normally free to move in any direction.

The Manoharan team was interested in getting closer with a scanning tunnel microscope, or STM – a tool that can identify and even move individual atoms in the top pair of atomic layers of a material.

Interaction places

The stripes, they discovered, apparently had nothing to do with the way the atoms of the material were organized, or with small bumps and droplets on the surface.

“Instead, the stripes were low where electrons act as if they were confined to 2D, puddle-like areas in the material,” Parra said. “The distance between splashes is short enough so that the electrons can ‘see’ and communicate with each other in a way that enables them to move without resistance, which is the hallmark of superconductivity.”

The 2D puddles appeared when the scientists carefully adjusted the temperature and other conditions to the transition point where the superconductor would become an insulator.

Their observations are consistent with a theory of ’emerging electronic graininess’ in superconductors, developed by Nandini Trivedi of Ohio State University and colleagues.

“The predictions we made were contrary to the standard paradigm for superconductors,” Trivedi said. “The stronger a superconductor is, the more it needs energy to break the bond between its superconducting electron pairs – a factor we call the energy gap. But my group predicted that in this particular type of disturbed superconductor, the opposite would be true. : the system would form emerging ponds where superconductivity was strong, but the pairs could be broken with much less energy than expected.

“It was quite exciting to see the predictions confirmed by the Stanford Group’s STM measurements!”

The spread of science

The results have practical implications for the production of 2D materials, Parra said.

“Most of the methods of making 2D materials are engineering approaches, such as thickening films of a few atomic layers or creating a sharp interface between two materials and limiting a 2D state there,” he said. she said. “It offers an extra way to get to these 2D superconducting states. It’s cheaper, you do not need luxury equipment that requires very low temperatures and it does not take days and weeks. The only tricky part is to compile the material just right. ‘

Parra now heads a laboratory at the Federico Santa María Technical University in Valparaíso, Chile, focusing on interdisciplinary studies of biological materials on nanoscale. She recently received an award to acquire and operate the first low-temperature scanning tunnel microscope in South America, which she plans to use to continue this line of research.

‘If I had this equipment in the lab,’ she said, ‘I would connect it to all the things I learned in Hari’s lab, and use it to teach a new generation of researchers that we work in nanoscience and nanotechnology. in Chile. ‘