This illustration depicts atomic vibrations, or phonons, in the crystalline lattice structure of manganese bismuth telluride. Image: Penn State.
This illustration depicts atomic vibrations, or phonons, in the crystalline lattice structure of manganese bismuth telluride. Image: Penn State.

As well as being one of the oldest technologies known to humans, magnetism is also at the forefront of new-age materials that could lead to next-generation lossless electronics and quantum computers. A team led by researchers at Penn State and the University of California (UC) San Diego has now discovered a new ‘knob’ for controlling the magnetic behavior of one promising quantum material, and their findings could pave the way toward novel, efficient and ultra-fast devices.

“The unique quantum mechanical make-up of this material – manganese bismuth telluride – allows it to carry lossless electrical currents, something of tremendous technological interest,” said Hari Padmanabhan, who led the research as a graduate student at Penn State. “What makes this material especially intriguing is that this behavior is deeply connected to its magnetic properties. So, a knob to control magnetism in this material could also efficiently control these lossless currents.”

Manganese bismuth telluride is a two-dimensional (2D) material made up of atomically thin stacked layers. It is an example of a topological insulator, an exotic material that can simultaneously be an insulator and a conductor of electricity. Importantly, because this material is also magnetic, the currents conducted around its edges could be lossless, meaning they do not lose energy in the form of heat. Finding a way to tune the weak magnetic bonds between the layers of the material could unlock these functions.

In a paper in Nature Communications, the researchers report that phonons, which are tiny vibrations of atoms, in the material may be one way to achieve this. “Phonons are tiny atomic wiggles – atoms dancing together in various patterns, present in all materials,” Padmanabhan said. “We show that these atomic wiggles can potentially function as a knob to tune the magnetic bonding between the atomic layers in manganese bismuth telluride.”

The researchers at Penn State studied manganese bismuth telluride using a technique called magneto-optical spectroscopy. This involves shooting a laser onto a sample of the material and measuring the color and intensity of the reflected light, which carries information about the atomic vibrations. With this technique, the researchers were able to observe how the vibrations changed as they altered the temperature and magnetic field.

This revealed that altering the magnetic field changed the intensity of the phonons. According to the researchers, this is due to the phonons influencing the weak inter-layer magnetic bonding.

“Using temperature and magnetic field to vary the magnetic structure of the material – much like using a refrigerator magnet to magnetize a needle compass – we found that the phonon intensities were strongly correlated with the magnetic structure,” said Maxwell Poore, a graduate student at UC San Diego and co-author of the paper. “Pairing these findings with theoretical calculations, we inferred that these atomic vibrations modify the magnetic bonding across layers of this material.”

Scientists at UC San Diego conducted experiments to track these atomic vibrations in real time. Phonons oscillate faster than a trillion times a second, many times faster than modern computer chips. A 3.5 gigahertz computer processor, for example, operates at a frequency of 3.5 billion times per second.

“What was beautiful about this result was that we studied the material using different complementary experimental methods at different institutions and they all remarkably converged to the same picture,” said Peter Kim, a graduate student at UC San Diego and co-author of the paper.

Further research is needed to directly use the magnetic knob, the researchers said. But if that can be achieved, it could lead to ultra-fast devices that can efficiently and reversibly control lossless currents.

“A major challenge in making faster, more powerful electronic processors is that they heat up,” said Venkatraman Gopalan, professor of materials science and engineering and physics at Penn State, and a co-author of the paper. “Heating wastes energy. If we could find efficient ways to control materials that host lossless currents, that would potentially allow us to deploy them in future energy-efficient electronic devices.”

This story is adapted from material from Penn State, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier. Link to original source.