Could a Magnetic Sandwich Make Your Electronic Devices Work More Efficiently?

The Science

Newswise — Scientists are continually searching for ways to increase computers’ power while reducing their electricity use. A big step forward would be finding a material that conducts electrons with near-zero resistance at normal operating temperatures. In this work, researchers found a promising candidate in a layered "sandwich" structure that exhibits a rare phenomenon known as the quantum anomalous Hall (QAH) effect. In this effect, electrons with their spins all aligned in the same direction can travel along the edges of a material with almost no resistance.

The Impact

Powerful computers have huge benefits, but they come at a significant energy cost. The sandwich structure studied here opens a new door to devices that can make use of the electron spin. Such devices would be faster and more powerful yet consume very little energy. More generally, the work helps scientists learn more about the atomic-level interactions that take place in stacks of layered materials. Such knowledge will help scientists and engineers design structures that push zero-resistance materials toward higher temperatures.

Summary

This research studied bismuth telluride (Bi₂Te₃), a topological insulator. This means that the material is electrically insulating in its interior but can conduct electrical currents on its surfaces. To turn a topological insulator (which includes both spin-up and spin-down currents) into a QAH insulator (with currents of just one type of spin), it is necessary to induce magnetic order in the material. Adding dilute amounts of magnetic dopants can be a challenging process that actually results in magnetic disorder, greatly suppressing the temperature at which the QAH effect can be observed. A better strategy is to sandwich the topological insulator with ferromagnetic layers, inducing magnetic order via proximity effects. One promising architecture involves a sandwich structure with single layers of the ferromagnetic insulator, manganese bismuth telluride (MnBi₂Te₄), on either side of layers of the ultrathin topological insulator, Bi₂Te₃.

At the Advanced Light Source, a Department of Energy (DOE) Office of Science light source user facility, researchers synthesized this sandwich structure with a process called molecular beam epitaxy, where atomic layers are carefully built up one at a time from sources of the different constituent materials. The samples were then transferred to an interconnected experimental chamber to probe the system’s electronic behavior using ultraviolet light. By examining the electrons that are emitted from the surface in response to the incident light, the researchers found features consistent with the predicted QAH effect, indicating that this quantum material sandwich is a good candidate for supporting the QAH effect at elevated temperatures.

Funding

Funding for this research included the Australian Research Council, Australia's Nuclear Science and Technology Organisation, and the Singapore Ministry of Education. The research used resources at the Advanced Light Source, a Department of Energy Office of Science user facility.