Spectacular advances in quantum computing, smartphones that only need to be charged once a month, trains that levitate and move at superfast speeds. Technological leaps like these might revolutionize society, but they remain largely out of reach until superconductivity – the flow of electricity without resistance or waste of energy – is fully understood.
One of the major limitations of real-world applications of this technology is that the materials that make superconductivity possible typically need to be at extremely cold temperatures to achieve this level of electrical efficiency. To work around this limitation, researchers need to establish a clear picture of what different superconducting materials look like on the atomic scale as they go through different states of matter to become superconductors.
Researchers at a Brown University lab, working with an international team of scientists, have taken a small step closer to unraveling this mystery for a recently discovered family of superconducting Kagome metals. In a new study, they used an innovative new strategy combining nuclear magnetic resonance imaging and quantum modeling theory to describe the microscopic structure of this superconductor at 103 degrees Kelvin, which is equivalent to regarding 275 degrees below 0. degrees Fahrenheit.
Researchers have described the properties of this bizarre state of matter for what is believed to be the first time in Physical examination research. Ultimately, the findings represent a new achievement in a steady march toward superconductors that operate at higher temperatures. Superconductors capable of operating at room temperature (or close to it) are considered the holy grail of condensed matter physics because of the tremendous technological opportunities they would open up in terms of energy efficiency, especially in transmission. electricity, transport and quantum computing.
“If you ever plan to design something and make it commercial, you have to know how to control it,” said physics professor Vesna Mitrovi?, who leads a condensed matter NMR group at the university and is co-author of the new study. “How do we describe it? How do we modify it to get what we want? Well, the first step is to know what the states are under the microscope. You need to start building a full picture of it. ”
The new study focuses on the superconductor RbV3Sb5, composed of the metals rubidium, vanadium and antimony. The material owes its namesake to its particular atomic structure, which resembles a basketwork pattern that features interconnected star-shaped triangles. Kagome materials fascinate researchers because of the understanding they provide of quantum phenomena, bridging two of the most fundamental areas of physics – topological quantum physics and condensed matter physics.
Previous work by different groups has established that this material goes through a cascade of different phase transitions when the temperature is lowered, forming different states of matter with different exotic properties. When this material is raised to 103 degrees Kelvin, the lattice structure changes and the material exhibits what is called a charge density wave, where the electrical charge density jumps up and down. Understanding these jumps is important for the development of theories describing the behavior of electrons in quantum materials such as superconductors.
What had not been seen before in this type of Kagome metal was what the physical structure of this lattice and charge order looked like at the temperature the researchers were looking at, which is the highest temperature state where the metal begins to transition between different states of matter. .
Using a new strategy combining NMR measurements and a modeling theory known as density functional theory which is used to simulate the electrical structure and position of atoms, the team was able to describe the new structure in which transforms the lattice and its charge density wave.
They showed that the structure changes from a 2x2x1 pattern with a characteristic Star of David pattern to a 2x2x2 pattern. This happens because Kagome’s network reverses on itself when the temperature becomes extremely freezing. The new network it transforms into is made up largely of separate hexagons and triangles, the researchers showed. They also showed how this pattern connects when they take a plane of the RbV3Sb5 structure and rotate it, “looking at” it from a different angle.
“It’s like this one Kagome now becomes these complicated things that split in two,” Mitrovi? said. “It stretches the network so that the Kagome becomes this combination of hexagons and triangles in one shot, then in the next shot, following rotating it half a circle, it repeats. »
Probing this atomic structure is a necessary step to providing a full picture of the exotic states of matter into which this superconducting material transforms, the researchers said. They believe the findings will dig deeper into the question of whether this formation and its properties can aid superconductivity or whether it is something that should be removed to make better superconductors. The unique new technique they used will also allow researchers to answer a whole new set of questions.
“We know what it is now and our next job is to figure out what the relationship is to other weird low temperature phases – does it help, does it compete, can we control, can we make it happen at higher temperatures, if that’s helpful? “Mitrovi? said. “Then we continue to lower the temperature and learn more. »
The experimental research was led by Jonathan Frassineti, a joint graduate student between Brown and the University of Bologna, Pietro Bonfà of the University of Parma, and two Brown students: Erick Garcia and Rong Cong. Theoretical work was carried out by Bonfà while all materials were synthesized at the University of California, Santa Barbara. This research included funding from the National Science Foundation.
