Researchers have shown that superconductivity — a state in which certain materials conduct electricity without resistance — in a special form of graphene known as "magic-angle graphene" can be completely turned off by controlling interactions between electrons. This discovery, made by scientists from the National Graphene Institute at The University of Manchester and other institutions, highlights the importance of electron interactions in enabling superconductivity. The team used a device with two twisted layers of graphene, separated by less than a nanometer, but electronically independent. This setup allowed them to manipulate a process called "Coulomb screening" — where electrons shield each other from forces — more precisely than in earlier experiments, enabling them to observe how superconductivity changes when electron interactions are reduced. The researchers, including Dr. Julien Barrier, Professor Alexey Berdyugin, and Professor Sir Andre Geim, found that increasing the number of charge carriers in the neighboring graphene layer gradually weakened the superconducting properties of the magic-angle graphene. At high enough carrier densities, superconductivity was entirely eliminated. They also observed that other unique electronic states, known as "correlated insulating states," vanished under the same conditions. Their measurements showed that the critical temperature at which superconductivity occurs could be reduced by more than ten times through screening. This effect was much more pronounced than in earlier studies, indicating that electron interactions have a far greater influence on superconductivity in these materials than previously thought. The team compared their results with theoretical models. In conventional superconductors, where electrons pair up through vibrations in the material's crystal lattice (called phonon-mediated pairing), screening should have little effect or even slightly increase superconductivity. However, the researchers observed the opposite — superconductivity weakened significantly, which suggests that phonon pairing is not the main mechanism at play in magic-angle graphene. While the study does not pinpoint a single explanation for the pairing mechanism, it supports several unconventional theories involving collective behavior of electrons. The findings provide strong constraints for future research on superconductivity in these materials. The researchers attribute the strong effect to the extremely small distance between the superconducting layer and the layer used for screening, which allowed them to modify electron interactions more effectively. This setup enabled the team to control superconductivity at scales as small as 0.3 nanometers, a level of precision not previously achieved. They believe this method could also help resolve other unresolved questions in condensed matter physics, offering a new tool for studying complex electron interactions in materials.