Stacking Materials Gain Interesting Properties
You cannot always get what you want the way you want it, but sometimes by doing some more work, you can arrive at what you desire. This is the situation with graphene, a material with amazing electrical properties, making it ideal for electronics, but for its lack of a band gap. One way to potentially add a band gap to graphene is to build a multi-layer stack of graphene and other materials, which, as researchers at the University of Manchester have recently discovered, adds even more properties than expected.
Graphene is an atom-thick sheet of carbon that has amazing electron mobility, but because it lacks a band gap, it is very difficult to switch off a current with it. By placing a layer of boron nitride, which has a similar structure but different electrical properties, on top of it though, the graphene's properties can be modified. The Manchester researchers decided to analyze just how these properties change by measuring capacitance. They found that when a magnetic field is present, the original graphene spectrum will be recreated in small areas; an effect known as Hofstadter butterflies. Though the effect has been theorized before, the observations are much more contorted than theory predicts. This is because the electrons are not just affected by the material's landscape but by other electrons.
The researchers also discovered that at very low temperatures, the graphene will start acting as a ferromagnet, and this phenomenon occurs and disappears with the butterflies. As the researchers do not yet understand all of what is happening, they will suggest any possible applications for this new electronic system, but do expect more surprises.
Source: University of Manchester