Two layers of graphene showing individual atoms.

A stack of two graphene sheets, each composed of a layer of carbon atoms, can host electron combinations called excitons. Laguna Design/SPL

Materials science

Double sheets of carbon atoms coaxed to produce excitons

Detection could lead to the development of smaller and more-versatile lasers.

Physicists have spotted particle-like phenomena called excitons in stacked layers of carbon atoms.

An exciton is a pairing of a free electron and a positively charged hole. Theorists predict that excitons should occur in double layers of graphene, which are carbon sheets only one atom thick. But the difficulty of creating suitable graphene samples has made it difficult to observe the expected excitons.

Long Ju and Lei Wang of Cornell University in Ithaca, New York, and their colleagues encased a double layer of graphene between sheets of a two-dimensional insulator. Shining infrared light on the device, they detected an electric current flow when the material absorbed specific wavelengths of light, indicating that they had created excitons that had then split into their individual components.

The scientists demonstrated that they could alter the wavelength of light that generated the excitons by applying an electric field. The findings point to a way of creating miniature infrared detectors and lasers that could work across a range of wavelengths.