Scientists discover a ‘button’ to control the magnetic behavior of a quantum material

Magnetism, one of the oldest technologies known to man, is at the forefront of new age materials that could enable the next generation of lossless electronics and quantum computers. Researchers led by Penn State and the University of California, San Diego have discovered a new ‘button’ for controlling the magnetic behavior of a promising quantum material, and the results could pave the way for new efficient, ultra-fast devices.

“The unique quantum mechanical composition of this material – manganese-bismuth telluride – enables it to carry electrical currents without loss, which is of enormous technological interest,” said Hari Padmanabhan, who led the research as a graduate student at Penn State. “What makes this material particularly exciting is that this behavior is deeply linked to its magnetic properties. Thus, a button to control the magnetism of this material could also effectively control these currents without loss.”

Manganese-bismuth telluride, a 2D material composed of atomically thin stacked layers, is an example of a topological insulator, exotic materials that can simultaneously be insulators and conductors of electricity, the researchers said. It is important because this material is also magnetic, currents carried around its edges can be lossless, which means that they do not lose energy such as heat. Finding a way to adjust the weak magnetic bonds between layers of the material could unlock these features.

Small vibrations of atoms or phonons in the material could be a way to do this, the researchers reported on April 8 in the journal Nature communication.

“Phonons are small atomic motions – atoms dance together in different patterns, present in all materials,” Padmanabhan said. “We show that these atomic ripples can potentially act as a button to adjust the magnetic bond between atomic layers in manganese-bismuth telluride.”

Penn State researchers studied the material using a technique called magneto-optical spectroscopy – firing a laser on a sample of the material and measuring the color and intensity of the reflected light, which contains information about atomic vibrations. The team observed how the vibrations changed as they changed temperature and magnetic field.

By modifying the magnetic field, the researchers observed changes in the intensity of the phonons. This effect is due to phonons affecting the weak magnetic bond between the layers, the researchers said.

“By 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 phonon intensities were strongly correlated with magnetic structure,” said graduate student Maxwell Poore. at UC San Diego, and co-author of the study. “By combining these results with theoretical calculations, we deduced that these atomic vibrations alter the magnetic bond through the layers of this material.”

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

“The beauty of this result was that we studied the material using different complementary experimental methods at different institutions, and they all converged remarkably on the same picture,” said graduate student Peter Kim. ‘UC San Diego and co-author of the article. .

Further research is needed to use the magnetic button directly, the researchers said. However, if this can be achieved, it can lead to ultra-fast devices that can efficiently and reversibly control currents without loss.

“A major challenge in making faster and more powerful electronic processors is that they run heat,” said Venkatraman Gopalan, professor of materials science and engineering and physics at Penn State, a former adviser to Padmanabhan and co-author of the article. “Heating wastes energy. If we could find efficient ways to control materials that contain lossless power, it would potentially allow us to implement them in future energy-efficient electronic devices.”

The other Penn State researchers were Vladimir Stoica, research associate professor, Huaiyu “Hugo” Wang, graduate student, and Maxwell Wetherington, staff researcher, Materials Research Institute and Department of Materials Science and Engineering; and Seng Huat Lee, Research Assistant Professor, and Zhiqiang Mao, Professor, 2D Crystal Consortium and Department of Physics.

James Rondinelli, professor, Danilo Puggioni, assistant research professor, Mingqiang Gu, postdoc researcher, and Nathan Koocher, graduate student, Northwestern University, also contributed; Xijie Wang, Xiaozhe Shen, and Alexander Reid, researchers at SLAC National Accelerator Laboratory; Richard Averitt, Professor, University of California, San Diego; Richard Schaller, Staff Researcher, Argonne National Laboratory; and Aaron Lindenberg, Associate Professor, Stanford University.

The U.S. Department of Energy, the National Science Foundation, and the Army Research Office funded this research.

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