A team of researchers has made a remarkable breakthrough in spintronic technology, achieving a one-directional flow of spin-polarized current in a single-atom layer of thallium-lead alloys.
This advancement not only challenges traditional views of material interaction with light but also heralds the development of ultra-fine, environmentally friendly data storage for the future.
Groundbreaking Discovery in Spintronic Technology
Researchers Ibuki Taniuchi, Ryota Akiyama, Rei Hobara, and Shuji Hasegawa from the University of Tokyo have discovered a groundbreaking way to control the direction of spin-polarized currents in a single-atom layer of thallium-lead alloys when exposed to light at room temperature. This finding challenges conventional understanding, as single-atom layers were previously believed to be nearly transparent, meaning they interact minimally with light.
The study’s observation of a one-directional current flow opens the door to advancements far beyond ordinary diodes, potentially leading to environmentally friendly data storage solutions and ultra-thin, two-dimensional spintronic devices. The research was published on January 10 in ACS Nano.
Advancements in Diode Functionality
Diodes, essential components of modern electronics, work by restricting current flow to one direction. However, as devices become thinner, designing and manufacturing these components becomes increasingly complex. This is where spintronics — a field focused on manipulating the spin of electrons, often using light — comes into play. By exploring spintronics in such ultra-thin systems, researchers aim to uncover new phenomena that could revolutionize electronics and data storage technology.
“Spintronics had traditionally dealt with thicker materials,” says Akiyama. “However, we had been more interested in very thin systems because of their inherently exciting properties. So, we wanted to combine the two and investigate the conversion of light to spin-polarized current in a two-dimensional system.”
Innovations and Future Applications
The conversion of light to spin-polarized current is called the circular photogalvanic effect (CPGE). In the spin-polarized current, the spins of electrons align in one direction, restricting the flow of the electrical current to one direction depending on the polarization of light. The phenomenon is similar to conventional diodes in which the electrical current can only flow in one direction depending on the polarity of the voltage.
The researchers used thallium-lead alloys to see if this phenomenon could be observed even in layers as thin as a single atom (two-dimensional systems). They conducted the experiments in an ultra-high vacuum to avoid adsorption and oxidation of the material so that they could reveal its “true colors.” When the researchers irradiated the alloys with circular polarized light, they could observe the changes in direction and magnitude of the flowing electrical current.
“Even more surprisingly,” says Akiyama, “it was a spin-polarized current: the direction of the electron spin was aligned with the direction of the current due to the novel properties of these thin alloys.”
These thin alloys previously developed by the team showed unique electronic properties, giving the team a hint for the current study by chance. Armored with this new knowledge, Akiyama looks to the future.
“These results show that basic research is crucial for applications and development. In this study, we aimed to observe an optimized system. As the next step, in addition to searching for novel two-dimensional thin alloys with unique electronic properties, we would like to use a lower energy (terahertz) laser to narrow the excitation paths that induce CPGE. This way we could increase the conversion efficiency from light to spin-polarized current.”
Reference: “Surface Circular Photogalvanic Effect in Tl–Pb Monolayer Alloys on Si(111) with Giant Rashba Splitting” by Ibuki Taniuchi, Ryota Akiyama, Rei Hobara and Shuji Hasegawa, 10 January 2025, ACS Nano.
DOI: 10.1021/acsnano.4c08742
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