Credit: Image courtesy of David Cobden
An exotic state of matter called a topological insulator has been observed in 3-D materials and artificial nanostructures, but not in simple 2-D materials—until now. The sketch shows a transistor made of a single layer of tungsten ditelluride, platinum electrical contacts (gray bars), and an insulating material (blue) that provides air-tight encapsulation. Voltage is applied to the graphene sheets (dark grey) on the top and bottom to control the sheet conductivity. When the conductivity is very low, the current between the contacts flows only at the edge of the 2-D material—as expected for a 2-D topological insulator!