The University of Chicago Pritzker School of Molecular Engineering (PME) has made significant progress in developing a new optical memory for quickly and energy-efficiently storing and accessing computational data.
During their study of a complex material made of manganese, bismuth, and tellurium (MnBi2Te4), researchers discovered that the material’s magnetic properties changed rapidly and easily in response to light. This breakthrough indicates that a laser could be utilized to encode information within the magnetic states of MnBi2Te4.
“This really underscores how fundamental science can enable new ways of thinking about engineering applications very directly,” said Shuolong Yang, assistant professor of molecular engineering and senior author of the new work. “We started with the motivation to understand the molecular details of this material and ended up realizing it had previously undiscovered properties that make it very useful.”
In a recent publication in Science Advances, Yang and colleagues demonstrated how the electrons in MnBi2Te4 are in competition between two conflicting states—a topological state ideal for encoding quantum information and a light-sensitive state suited for optical storage.
MnBi2Te4 has garnered attention for its potential as a magnetic topological insulator (MTI), a material that acts as an insulator internally but conducts electricity on its outer surfaces. In the 2D limit, an intriguing quantum phenomenon occurs, where an electric current flows in a two-dimensional stream along its edges, forming “electron freeways” capable of encoding and carrying quantum data.
Though the prediction is that MnBi2Te4 can host such an electron freeway, experimental work with the material has been challenging. To tackle this issue, Yang’s group employed advanced spectroscopy methods to observe the behavior of electrons within MnBi2Te4 in real time on ultrafast time scales.
This involved using time- and angle-resolved photoemission spectroscopy developed in the Yang lab, along with collaborating with Xiao-Xiao Zhang’s group at the University of Florida for time-resolved magneto-optical Kerr effect (MOKE) measurements, enabling the observation of magnetism.
“This combination of techniques gave us direct information on not only how electrons were moving, but how their properties were coupled to light,” explained Yang.
Upon analyzing the spectroscopy results, the researchers discovered why MnBi2Te4 was not an ideal topological material. They found a competing quasi-2D electronic state vying for electrons with the topological state.
“There are completely different types of surface electrons that replace the original topological surface electrons,” said Yang. “But it turns out that this quasi-2D state actually has a different, very useful property.”
Interestingly, the second electronic state showed a strong correlation between magnetism and external photons of light, making it unsuitable for sensitive quantum data but perfectly suited for efficient optical memory.
To explore this potential application, Yang’s group plans to conduct experiments using a laser to manipulate the material’s properties. They anticipate that an optical memory utilizing MnBi2Te4 could surpass today’s electronic memory devices in efficiency by several orders of magnitude.
Moreover, a better understanding of the balance between the two electron states on the surface of MnBi2Te4 could significantly enhance its potential as a topological insulator and make it valuable for quantum data storage.
“Perhaps we could learn to tune the balance between the original, theoretically predicted state and this new quasi-2D electronic state,” he said. “This might be possible by controlling our synthesis conditions.”
Journal reference:
- Khanh Duy Nguyen, Woojoo Lee, Jianchen Dang, Tongyao Wu, Gabriele Berruto, Chenhui Yan, Chi Ian Jess Ip, Haoran Lin, Qiang Gao, Seng Huat Lee, Binghai Yan, Chaoxing Liu, Zhiqiang Mao, Xiao-Xiao Zhang, Shuolong Yang. Distinguishing surface and bulk electromagnetism via their dynamics in an intrinsic magnetic topological insulator. Science Advances, 2024; DOI: 10.1126/sciadv.adn5696
