A sheet of germanane just one atom thick sits on a piece of germanium, and current races across it like a highway with no traffic lights. Germanane is a flat lattice of germanium atoms covered with hydrogen, a cousin of graphene. On its own, it's a semiconductor, but at the interface with bulk germanium, a thin layer forms where holes (empty spots for electrons that behave like positive charges) fly almost unimpeded.
At 15 kelvins (minus 258°C), hole mobility hit 67,000 square centimeters per volt-second. For comparison, in silicon, the stuff of computer chips, that number is hundreds of times lower. Between 20 and 250 kelvins, holes move as if in a metal, with impurities barely getting in the way. A magnetic field of 7 teslas (140,000 times stronger than Earth's) changes the resistance by a factor of 66, and quantum oscillations are visible — ripples in the graph proving that the holes are confined to a flat layer.
This layer doesn't require complex technology: you simply place a 2D sheet on a 3D crystal of the same element. It's like making a sandwich with two kinds of bread without baking them together. Previously, fast holes required growing multilayer structures with atomic precision; here, a simple contact sufficed. Now engineers have an easy recipe for transistors, sensors, and other devices that need fast current at low voltage.
Germanane is an analog of graphene, but made from germanium. Unlike the carbon sheet, it has a band gap, so it can work as a transistor, not just a conductor.