Using their newly-developed microscopy method with four movable probing tips, scientists at ORNL have observed the spin behavior of electrons on the surface of a topological insulator. Image: Saban Hus and An-Ping Li/Oak Ridge National Laboratory, US Dept. of Energy.A new method for precisely measuring the mysterious behavior and magnetic properties of electrons flowing across the surface of quantum materials could open a path to next-generation electronics.
Found at the heart of electronic devices, silicon-based semiconductors rely on a controlled electrical current. At the moment, these semiconductors can only access the electrons' charge for energy, but electrons do more than carry a charge. They also have intrinsic angular momentum known as spin, which is a feature of quantum materials that, while elusive, can be manipulated to enhance electronic devices.
A team of scientists, led by An-Ping Li at the US Department of Energy's Oak Ridge National Laboratory (ORNL), has now developed an innovative microscopy technique that can detect the spin of electrons in topological insulators. These are a new kind of quantum material that could be used in applications such as spintronics and quantum computing.
"The spin current, namely the total angular momentum of moving electrons, is a behavior in topological insulators that could not be accounted for until a spin-sensitive method was developed," Li said.
Electronic devices continue to evolve rapidly and require more power packed into smaller components, prompting the search for less costly, energy-efficient alternatives to charge-based electronics. A topological insulator carries electrical current along its surface, while acting as an insulator deeper within the bulk material. Electrons flowing across the material's surface exhibit uniform spin directions, unlike in a traditional semiconductor where electrons spin in varying directions.
"Charge-based devices are less energy efficient than spin-based ones," said Li. "For spins to be useful, we need to control both their flow and orientation."
To detect and better understand this quirky particle behavior, the team needed an analytical method that was sensitive to the spin of moving electrons. They came up with a new microscopy method that builds on a four-probe scanning tunneling microscope – an instrument that can pinpoint a material's atomic activity with four movable probing tips – by adding a component to observe the spin behavior of electrons on the material's surface. This approach not only allows measurements of spin sensitivity, but also confines the current to a small area on the surface, which helps to keep electrons from escaping beneath the surface and thus ensure high-resolution results.
The scientists tested their new microscopy method on a single crystal of Bi2Te2Se, a topological insulator containing bismuth, tellurium and selenium. It allowed them to measure how much voltage was produced along the material's surface as the flow of electrons moved between specific points, while also sensing the voltage for each electron's spin.
"We successfully detected a voltage generated by the electron's spin current," said Li, who co-authored a paper in Physical Review Letters that explains the method. "This work provides clear evidence of the spin current in topological insulators and opens a new avenue to study other quantum materials that could ultimately be applied in next-generation electronic devices."
This story is adapted from material from ORNL, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier. Link to original source.