"Magic-angle" graphene uses faint light to turn insulator into metal
A team at the National University of Singapore has turned magic-angle twisted bilayer graphene from an insulator into a metal using only faint long-wavelength light, pointing to a new class of terahertz and far-infrared detectors.
Researchers have demonstrated that "magic-angle" twisted bilayer graphene can transition from an insulator to a metal when exposed to faint light. This discovery highlights a unique quantum effect that could lead to the development of highly sensitive detectors for faint terahertz and far-infrared radiation. The study, published in Nature Communications, focuses on magic-angle twisted bilayer graphene (MATBG), created by stacking and rotating two graphene sheets at a specific angle.
In their experiments, scientists found that low-intensity, long-wavelength radiation can melt the fragile correlated insulating state of MATBG, significantly reducing its electrical resistance. This transition occurs even with relatively weak radiation, contrasting with previous methods that required intense, ultrafast excitation to achieve similar effects.
The potential applications of this discovery are vast, including security imaging, material inspection, astronomy, and environmental sensing. The researchers used a device consisting of magic-angle graphene sandwiched between layers of hexagonal boron nitride, configured as a field-effect transistor, and controlled by a graphite back gate.
When exposed to millimeter-wave and far-infrared radiation, the graphene's low-heat-capacity electronic system was heated by incoming photons. This small temperature increase destabilized the cooperative electronic order, collapsing the insulating gap and transforming the material into a metal.
The device's response to radiation was similar to superconducting bolometers, but with a reverse mechanism. Instead of destroying a zero-resistance state, the photons disrupted a high-resistance correlated insulating state, turning it metallic. This insulator-to-metal transition serves as the detector's signal, responding to wavelengths from 85 to 2,140 micrometers.
This portion of the electromagnetic spectrum is valuable for revealing information that ordinary cameras cannot, such as penetrating materials opaque to visible light and providing insights into material composition.
Source: Graphene Feed