Researchers at the Institute for Functional Intelligent Materials (I-FIM) at Singapore's National University of Science and Technology (NUS) have made progress in understanding how electrical resistance in twisted bilayer graphene arises. In a study published in Nature Communications on August 13, 2026, the team developed a method to isolate the effects of electron collisions and lattice vibrations on resistance. Using terahertz radiation, they heated the electrons without warming the surrounding lattice, allowing them to observe a significant increase in resistance. This revealed that electronic interactions, rather than lattice vibrations, play a major role in resistance even in conditions where lattice vibrations are usually dominant. Twisted bilayer graphene is made by stacking two graphene layers at a very small angle, typically about 1.1 degrees, known as the "magic angle." At this angle, the material's electronic structure changes dramatically, leading to unusually flat energy bands. This flatness enhances electron interactions, giving rise to exotic properties such as superconductivity and correlated insulating states. These effects complicate the interpretation of resistance measurements, which are often based on temperature changes. To study the behavior of electrons in this material, the researchers built devices with twisted graphene layers encapsulated in hexagonal boron nitride, a material that helps preserve the graphene's properties. Metal antennas were used to direct terahertz radiation at the samples, heating the electrons without significantly warming the lattice. The results showed that when electrons were heated, resistance increased substantially — a phenomenon known as photoresistance. This increase became more pronounced with higher terahertz power, though it eventually plateaued. Near the magic angle, resistance increased by several kilohms, indicating strong electronic effects. In devices twisted at angles farther from the magic angle, the team observed a typical T² resistance behavior at low charge carrier densities, which is usually linked to electron-electron collisions. However, traditional mechanisms for current dissipation, like umklapp scattering and collisions between different carrier bands, were not present at these low densities. Instead, the researchers proposed that collisions between different "valleys" in the electronic band structure — regions of momentum space — could alter electron velocities enough to reduce current, even while overall momentum is conserved. The study highlights that electronic interactions are a key factor in limiting current flow in both magic-angle and higher-twist-angle regimes. The use of terahertz radiation to separately control electron and lattice temperatures offers a new way to study quantum transport in complex materials. This method could be applied to other moiré systems and low-density quantum materials, helping researchers better understand the dominant scattering mechanisms and improve models of charge transport in correlated materials.