Quantum electronics: Charge travels like light in double-layer graphene

An international research team led by the University of Göttingen has experimentally demonstrated that electrons in naturally occurring double-layer graphene move like particles without any mass, just like light propagates. In addition, they showed that electric current can be “switched on” and off, making it possible to develop tiny, energy-efficient transistors, like the light switches in your home, but at the nanometer scale.

The Massachusetts Institute of Technology (MIT) in the United States and the National Institute of Materials Science (NIMS) in Japan also participated in the research.The results were published in nature communications.

Graphene, discovered in 2004, is a single layer of carbon atoms. Among its many unusual properties, graphene is known for its extremely high electrical conductivity, which is due to the high and constant speed of electrons in this material. This unique capability has led scientists to dream of using graphene to create faster, more energy-efficient transistors.

The challenge is that in order to make a transistor, the material needs to be controlled to have a highly insulating state in addition to a highly conductive state. However, in graphene, this “switching” of carrier speed is not easy to achieve. The fact that graphene generally does not have an insulating state limits its potential as a transistor.

The University of Göttingen team has now discovered that two graphene layers, found in the natural form of bilayer graphene, combine the best of both worlds: a structure that supports electrons moving as fast as light, as if they had no mass, except insulation status. The researchers showed that this could be changed by applying an electric field perpendicular to the material, making the two-layer graphene insulating.

This property of fast-moving electrons had been predicted theoretically as early as 2009, but because my materials were provided by NIMS and I worked closely with MIT on the theory, the sample quality was significantly improved, making it possible to experimentally to identify this characteristic. Although these experiments were performed at low temperatures (about 273° below freezing), they show the potential of double-layer graphene to create highly efficient transistors.

“We already knew this theory. However, now we have performed experiments that actually show light-like dispersion of electrons in double-layer graphene. This is a very exciting moment for the entire team,” says Professor Thomas Göttingen. Thomas Weitz, University School of Physics.

Dr. Anna Seiler, postdoctoral researcher at the University of Göttingen and first author, added: “Our work is only a first step, but a crucial one. The next step for the researchers will be to see whether bilayer graphene is actually Transistors could be improved or the effect could be studied for its potential in other areas of technology.