Heterostructures are different layers of atoms stacked on top of each other to form a single structure. They were first proposed in 1959 by the physicist Richard Feynman, who famously asked: “What would the properties of materials be if we could arrange atoms just the way we want them?”
Over the following decades, researchers developed the ability to engineer the arrangement of atoms through which particles such as electrons (particles of charge) or photons (particles of light) travel.
This allowed scientists to probe, understand, and eventually control the quantum mechanical properties of the particles – the behaviour of matter and light – creating a toolkit for the technological development of electronics and photonics.
Today, heterostructures are everywhere; they enable technologies such as transistors in computers, solar cells, LED lighting, and lasers. Even the internet would not be possible without use of heterostructures.
Until now, our use of heterostructures has been limited to taking advantage of isolated, individual particles, where their interactions are negligible.
However, if scientists could understand and take control of the interactions between particles within heterostructures, unimagined new technologies will become possible.
Like dancers in a ballet, interacting particles can coordinate their movements in surprising ways. Strongly interacting electrons can: dance together in their place to generate strong magnets; completely stop their journey through a crystal as if frozen to create insulators; or pair up to zoom through a crystal without any resistance to create a superconductor.
Unfortunately, the precise steps in the choreography of interacting particles are tricky to control, and in many cases not even well understood, which prevents their implementation in technologies.
However, an unexpected recent discovery has renewed optimism that this difficult problem can now be tackled.
If two sheets of carbon atoms, called ‘graphene’, are placed on top of each other with a relative twist of precisely 1.1 degrees – the so-called “magic angle” – an abundance of correlated electron states miraculously appear.
Graphene, the wonder material found in graphite pencil lead, is completely non-magnetic and does not host strongly correlated states. However, when two layers are stacked at the magic angle, it can be switched from insulating to magnetic to superconducting with the use of a tiny battery.
The discovery of these astonishing features is now driving a revolution in our ability to produce, study, and take advantage of heterostructures.
Through these ventures into strongly correlated quantum materials, a whole new generation of low-energy technologies and tools, beyond anything we can currently imagine, becomes ever more likely.
Brian Gerardot is professor at the Institute of Photonics and Quantum Science at Heriot-Watt University, a current chair in emerging technologies at the Royal Academy of Engineering, and a fellow of the Royal Society of Edinburgh. This article expresses his own views. The RSE is Scotland's national academy, bringing great minds together to contribute to the social, cultural and economic well-being of Scotland. Find out more at rse.org.uk and @RoyalSocEd.