Superconductivity in magic-angle twisted bilayer graphene can be completely suppressed by screening the electrical interactions between its electrons, according to researchers at the University of Manchester’s National Graphene Institute and the National University of Singapore. The finding provides strong experimental evidence that electron-electron interactions drive the pairing behind the material’s superconductivity, addressing a central question in physics since the phenomenon was first discovered.
The Mechanics of Sub-Nanometer Screening
Lead author Julien Barrier explained that testing this hypothesis required overcoming significant experimental hurdles. The team had to build a device where a tunable screening layer sat a fraction of a nanometer away from the superconducting graphene while remaining electronically separate. According to Barrier, the researchers used a twisted graphene bilayer in atomic contact with the magic-angle graphene to achieve this precision.
“When we switched on the screening, we were surprised to find that superconductivity was completely suppressed,” said corresponding author Professor Alexey Berdyugin of the National University of Singapore. Berdyugin noted that this sub-nanometer screening technique, operating over distances as short as 0.3 nanometers, offers a new opportunity to understand electronic interactions in high-temperature superconductors and other complex materials.
Challenging Conventional Phonon Models
This suppression runs counter to what conventional phonon-mediated superconductivity would predict. Standard models assume that screening Coulomb repulsion between electrons should leave phonon-coupled pairing unchanged or slightly enhance it. By comparing their results against theoretical modeling, the team found the observed suppression aligns with pairing driven by electron-electron interactions, such as electron-plasmon coupling, rather than atomic vibrations.
Contributing researchers from the Henry Royce Institute, Washington University in St. Louis, the University of Pennsylvania, the University of Antwerp, and Japan’s National Institute for Materials Science collaborated on the study. While the data points toward electron-electron pairing, the authors noted that the work does not single out one definitive unconventional mechanism among several consistent models.
Broader Implications for Twistronics and Room-Temperature Goals
Corresponding author Professor Sir Andre Geim emphasized the long-term motivation behind the research. “Personally, I am interested only in high-temperature superconductivity – preferably at room temperature or above,” Geim said. He acknowledged that the study was conducted at extremely low temperatures, where helium turns liquid, but added that understanding the core mechanism is vital to eventually reaching room-temperature applications.
This development builds on foundational discoveries in “twistronics,” a field launched in 2018 when Pablo Jarillo-Herrero and his MIT team first demonstrated magic-angle twisted bilayer graphene. MIT researchers have continued exploring these systems, recently showing that magic-angle graphene stacked between boron nitride layers can switch superconductivity on and off via short electric pulses rather than continuous fields.
Did you know?
Magic-angle graphene is created by stacking two atom-thin sheets of carbon at a precise, twisted angle, forming a moiré superlattice that generates exotic electronic states like insulating behavior and superconductivity.
Frequently Asked Questions
What causes superconductivity in magic-angle graphene?
Recent experiments show that strong electron-electron interactions drive the pairing mechanism, ruling out traditional atomic vibration models.
How did researchers suppress the superconductivity?
Researchers placed a tunable screening layer just 0.3 nanometers away from the superconducting graphene, which completely suppressed the phenomenon when activated.
Why is this research important for future electronics?
Understanding the fundamental pairing mechanisms in twisted two-dimensional materials brings physicists closer to developing room-temperature superconductors and energy-efficient electronic devices.
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