Researchers at the National University of Singapore’s Institute for Functional Intelligent Materials (I-FIM) published findings in Nature Communications on August 13, 2026, demonstrating that electron-electron interactions, rather than atomic lattice vibrations, primarily limit electrical current in twisted bilayer graphene when electronic systems are heated via terahertz radiation.
Isolating Hot Electrons from a Cold Atomic Lattice
When current moves through a standard conductor, electrical resistance typically climbs as thermal energy increases. Pinpointing the exact microscopic culprit behind that resistance has long frustrated solid-state physicists. Traditionally, standard temperature tests warm both the charge-carrying electrons and the surrounding atomic lattice simultaneously. Because both components heat up together, their physical fingerprints become inextricably superimposed in the final resistance measurement.
To untangle these competing variables, the research team at NUS I-FIM utilized terahertz radiation. As detailed in work published on August 13, 2026, metal antennas channeled 0.14-terahertz radiation into tiny bar-shaped devices made of twisted bilayer graphene encapsulated in hexagonal boron nitride. Graphite gates simultaneously regulated the charge carrier density.
Each individual terahertz photon carried precisely 0.6 millielectronvolts of energy. This targeted delivery warmed the electronic system directly while leaving the surrounding atomic lattice virtually unchanged. According to I-FIM Principal Investigator Assistant Professor Denis Bandurin, who led the study, conventional methods fail because they heat electrons and the lattice at the same time. By splitting those two thermal domains, the team could finally observe what the electrons were doing on their own.
The Physics of the Magic Angle and Moiré Superlattices
Graphene consists of a single atomic layer of carbon structured in a strict honeycomb formation. Stacking two of these sheets together and introducing a slight rotational offset creates a larger secondary interference pattern known as a moiré superlattice. This overlapping geometry fundamentally alters the quantum energy landscape.
Near a rotational twist of approximately 1.1 degrees—known as the magic angle—specific electronic energy bands flatten out dramatically. Under these conditions, electrons slow down significantly and experience much stronger mutual electrostatic interactions. This flat-band regime enables the material to host exotic collective phenomena, including correlated insulating states and superconductivity.
However, this same geometry complicates basic electrical characterization. In a standard Fermi liquid description of metals, electron-electron interaction resistance scales with the square of temperature, often denoted as T-squared behavior. Conversely, a linear temperature-dependent resistance typically indicates scattering by phonons, which are quantized lattice vibrations. Twisted bilayer graphene frequently exhibits both signatures depending on carrier density and twist angle, leaving temperature curves open to multiple interpretations.
Experimental Observations and Electronic Resistance
By applying targeted terahertz excitation to devices twisted near the magic angle, the researchers tracked a direct electrical response independent of lattice heating. The material’s resistance climbed by several kilo-ohms. This sharp upward shift revealed a dominant electronic contribution to scattering, even in experimental regimes traditionally attributed primarily to phonon activity.
Artur Shilov, an I-FIM PhD student and first author of the research paper, noted that twisted bilayer graphene often yields identical temperature dependencies from multiple distinct microscopic origins. Utilizing targeted carrier heating provided the necessary control knob to distinguish between electron-phonon scattering and internal electronic collisions.
The separation of these thermal channels offers a clearer baseline for understanding quantum transport in two-dimensional materials.
