WVU physicists discover electron interactions in quantum materials

Researchers at WVU and the University of Chicago Pritzker School of Molecular Engineering have discovered that adjusting the ratio of elements in iron telluride selenide allows them to switch exotic quantum states on and off in the material. The material possesses superconductivity as well as certain exotic properties and is typically grown in ultra-thin films for quantum computing applications. By tweaking the chemical recipe and changing the interactions between electrons in the films, the researchers could tune the elements and move them between different quantum phases. They were also able to reach a highly desirable state called a topological superconductor. Topological superconductors are promising for building error-free quantum devices because they are inherently stable and resistant to the noise that affects most quantum materials. Coauthor Subhasish Mandal, assistant professor in the Department of Physics and Astronomy at the WVU Eberly College of Arts and Sciences, explained that today's most powerful computers hit a wall when tackling certain problems from designing new drugs to cracking encryption codes. Error-free quantum computers promise to overcome those challenges, but building them requires materials with the exotic properties of topological superconductors. The research team included University of Chicago collaborators Shuolong Yang, assistant professor of molecular engineering, and graduate student Haoran Lin. Their findings, published in Nature Communications, reveal that as the ratio of tellurium and selenium changes in iron telluride selenide, so do the correlations between different electrons. Changing those ratios serves as a sensitive control knob for engineering exotic quantum phases. Mandal noted that iron telluride selenide is a unique material because it brings together superconductivity itself, strong spin-orbit coupling, and pronounced electronic correlations. This combination makes it an ideal system in which to explore how different quantum effects interact and compete, he said. The team noted that overly strong correlations pin electrons in place, while overly weak interactions wash out the material's topological features. At the right strength, these interactions give rise to topological superconductivity. Christopher Jacobs, a graduate student in Mandal's group, turned to advanced computational methods to explain the transition. Jacobs realized that the motion of electrons changed as tellurium concentrations increased, and that those changing electron correlations drove the quantum states and the way electrons behaved on the material's surface. Seeing this delicate balance unfold experimentally was both surprising and illuminating, Mandal said. It points to electron correlations as a powerful and previously underappreciated tool for engineering topological quantum matter, he said. It also highlights the fact that quantum materials are not fixed objects and can be actively tuned by subtle internal interactions.