Faint infrared light triggers quantum switch in magic-angle graphene

Matter transforms. We know this from childhood—ice melts, steam condenses, wax softens in heat. These everyday shifts happen because atoms physically rearrange themselves, trading one structure for another. But there exists a stranger category of transformation, one that happens at the scale of electrons rather than atoms. A quantum material can undergo a complete change in behavior—from insulator to conductor, from one electrical property to its opposite—without any visible rearrangement at all. Only the electrons reorganize, responding to the subtlest nudge: a shift in temperature, a change in magnetic field, or a beam of light.

Superconductors have long been the poster child for this kind of electronic phase transition. For more than a century, physicists have marveled at materials that suddenly lose all electrical resistance below a critical temperature, conducting current as if it were flowing through nothing at all. But what makes superconductors truly useful is not just the superconducting state itself—it is the transition point, that knife's edge where the material becomes exquisitely sensitive. The slightest external push at that threshold produces an enormous response. This hair-trigger sensitivity is why superconductors became the basis for some of the world's most precise detectors, instruments capable of catching individual photons arriving from the far reaches of space.

At the National University of Singapore, researchers in the CMX laboratory work with a different kind of quantum material, one that exhibits its own dramatic phase transition. They study magic-angle twisted bilayer graphene—a structure created by stacking two sheets of graphene and rotating one relative to the other by roughly one degree. At this precise angle, something remarkable happens: the electronic bands become extraordinarily narrow, and electrons interact with each other far more intensely than they normally would. Under the right conditions, these enhanced interactions produce a correlated insulator, a fragile collective state in which the material's ability to conduct electricity becomes severely suppressed.

In research published in Nature Communications, the team discovered that this fragile insulating state can be switched into a metallic state by exposing it to far-infrared radiation—and remarkably, only faint amounts are needed. The mechanism is elegantly simple. When far-infrared light strikes the material, it heats the electrons themselves while leaving the crystal lattice cold. This selective heating of the electron population is enough to destabilize the delicate insulating phase and restore metallic conduction. The material flips from one state to another, triggered by barely perceptible light.

The finding matters on two levels. For fundamental physics, it reveals something new about how these fragile quantum states behave—how they form, how they collapse, and how they respond to external control. Watching a correlated electron state dissolve under a whisper of infrared light opens a window into some of the most delicate collective behaviors in condensed matter physics. But beyond the laboratory curiosity lies a practical problem that has long frustrated scientists and engineers. Far-infrared radiation occupies an awkward middle ground in the electromagnetic spectrum, sitting between the domains of electronics and optics. It is notoriously difficult to generate and even harder to detect, yet it is precisely where many emerging technologies operate. Medical imaging systems rely on it. Security screening equipment uses it. Astronomers need it to observe the universe. Progress in all these fields has been bottlenecked by the lack of fast, sensitive detectors.

The magic-angle graphene platform offers a new solution. Because the insulating state can be switched on and off using a simple gate voltage, and because even minimal far-infrared light is sufficient to trigger the transition, the material becomes a tunable detector for a part of the spectrum that has remained largely out of reach. The researchers have essentially created a quantum switch—one that responds to the faintest infrared signals and can be controlled electronically. For fields ranging from medical diagnostics to security and astronomy, this represents a new tool for capturing and measuring radiation that has been difficult to work with for decades.