Researchers at the National University of Singapore, the Center for Neurophysics and Neuromorphic Technologies (Moscow), Queen's University (Kingston), HSE University (Moscow), the National Institute for Materials Science (Tsukuba) and the University of Manchester, have shown that magic-angle twisted bilayer graphene (MATBG) can be switched from an insulating to a metallic state by exposure to very weak far-infrared (FIR) radiation, opening a path toward ultrasensitive detectors for one of the least-exploited bands of the electromagnetic spectrum.
MATBG is formed by stacking two graphene sheets with a relative twist of about one degree. At this "magic" angle, the electronic bands narrow dramatically, strengthening interactions between electrons. Under the right gate voltage, these interactions produce a correlated insulator - a fragile collective electronic state in which conduction is strongly suppressed, distinct from an ordinary band insulator.
The team found that even low-intensity FIR radiation is enough to collapse this insulating state into a metallic one. The mechanism relies on the radiation selectively heating the electronic subsystem, which has low heat capacity, while the crystal lattice itself stays cold - a small rise in electron temperature is sufficient to suppress the correlated gap and restore conduction. This produces a broadband, low-noise photoresponse with voltage responsivity exceeding millivolts per nanowatt of absorbed power, and the effect remains robust under magnetic fields of several tesla.
The result is conceptually related to hot-electron detection mechanisms used in superconducting bolometers, but works in the opposite direction: rather than radiation destroying superconducting order, it destroys correlated insulating order to switch the material into a conductive state. The FIR range sits between the domains of conventional electronics and optics and remains difficult to generate and detect, despite its relevance to medical diagnostics, security screening, and astronomical observation - areas where progress depends on fast, sensitive detectors.
The authors note that the correlated insulating state in MATBG can be tuned on and off with a simple gate voltage, positioning the material as a new platform for FIR detection alongside superconducting approaches.
