Single-atomic metal layer reveals unexpected spin-polarized current control by light

Researchers at the University of Tokyo have demonstrated that the direction of spin-polarized current is restricted to only one direction in a single atomic layer of a thallium-lead alloy when irradiated at room temperature. This discovery overturns conventional wisdom, as it was thought that single atomic layers are almost completely transparent, meaning they absorb almost no light or interact with it.

The unidirectional current flow observed in this study enables functionality beyond ordinary diodes and paves the way for more environmentally friendly data storage, such as hyperfine two-dimensional spintronic devices in the future. . The results of this research are published in the journal ACS Nano.

Diodes are fundamental building blocks of modern electronics by restricting the flow of current in only one direction. However, as devices become thinner, the design and manufacturing of these functional components becomes more complex. Therefore, it is important to demonstrate the phenomena that may enable such developmental feats. Spintronics is a field of research in which researchers manipulate the intrinsic angular momentum (spin) of electrons, such as by shining light on them.

“Spintronics has traditionally worked with thicker materials,” says Ryota Akiyama. “But we were more interested in very thin systems because of their inherently excited properties. So we combined the two and applied the spin-polarized currents of light in two-dimensional systems. I wanted to investigate the transformation of

The conversion of light into spin-polarized current is called the circular photogalvanic effect (CPGE). In a spin-polarized current, the electron spins are aligned in one direction, and the current flow is restricted to one direction depending on the polarization of the light. This phenomenon is similar to traditional diodes, where current flows only in one direction depending on the polarity of the voltage.

The researchers used an alloy of thallium and lead to see if this phenomenon could be observed in layers as thin as a single atom (a two-dimensional system). They conducted experiments in ultra-high vacuum to avoid adsorption and oxidation of the material to reveal its “true color.” When the researchers illuminated the alloy with circularly polarized light, they were able to observe changes in the direction and magnitude of the current flowing through it.

“What was even more surprising was that it was a spin-polarized current. A new property of these thin alloys caused the direction of the electron spin to match the direction of the current,” Akiyama says.

These thin alloys, which the researchers had previously developed, exhibited unique electronic properties, which coincidentally inspired the researchers’ current work. Armed with this new knowledge, Akiyama looks to the future.

“These results demonstrate that fundamental research is important for application and development. In this study, we aimed to observe an optimized system. As a next step, we In addition to the search for new two-dimensional thin alloys with a lower energy (terahertz) laser, the efficiency of light-to-spin-polarized current conversion can be increased by narrowing the excitation path that causes CPGE. Masu.”

The research team included Ibuki Taniuchi, Akiyama, Rei Yasuhara, and Shuji Hasegawa.