Physics World, Hamish Johnston
The Physics World 2018 Breakthrough of the Year goes to Pablo Jarillo-Herrero of the Massachusetts Institute of Technology (MIT) in the US and colleagues for making the discovery that led to the development of “twistronics”, which is a new and very promising technique for adjusting the electronic properties of graphene by rotating adjacent layers of the material. The technique was first used by the team to create “magic-angle graphene”, which behaves like a high-temperature superconductor.
Graphene is a layer of carbon just one atom thick that has a honeycomb lattice. Bilayer graphene is a stack of two layers in which the two lattices are usually oriented in a specific way. Twistronics began when Jarillo-Herrero and colleagues discovered Mott insulator behaviour in pristine bilayer graphene when the orientation of the two layers were twisted by a magic angle.
The team, a collection of researchers from MIT, Harvard University and the National Institute of Materials Science (NIMS) in Japan, then showed that by adding electrons to the twisted bilayer using an applied electric field, they could make it superconducting.
The development of twistronics has already triggered several important follow-up discoveries in graphene research. Scientists at Columbia University devised a way to finely tune the angle between adjacent layers of 2D materials and thereby control the electronic properties. This highlights the potential for twistronics as an alternative paradigm for device engineering.
Further theoretical investigations have provided insights into the electronic transitions in bilayer and multilayer graphene systems. Theorists have highlighted the potential for unconventional superconductivity, including topological superconductivity and the existence of topological “Majorana states” at the edge of the material. These states could be particularly useful for creating quantum bits in quantum computers because they are more robust to environmental perturbations than many of the alternatives.
More recently, adding a twist between layers of 2D materials has also helped prevent Umklapp scattering, which degrades carrier mobility at high temperatures.