Revealing new insights into single-atom metal alloy properties

Revealing new insights into single-atom metal alloy properties
by Riko Seibo
Tokyo, Japan (SPX) Jan 13, 2025

Researchers from the University of Tokyo, led by Ibuki Taniuchi, Ryota Akiyama, Rei Hobara, and Shuji Hasegawa, have discovered a way to restrict the direction of spin-polarized current to a single direction in a single-atom layer of thallium-lead alloys at room temperature when irradiated with light. This finding challenges prior assumptions that single-atom layers are nearly transparent to light and offers potential for innovative spintronic devices and environmentally friendly data storage solutions.

Single-atom layers have generally been regarded as negligibly interactive with light, but the study reveals how a one-directional current flow in these materials could expand the functionality of diodes. Diodes are essential components in electronics, controlling current flow direction. However, as devices become thinner, designing and manufacturing such elements becomes increasingly complex. The observed phenomena suggest possibilities for advancing ultra-fine two-dimensional spintronic devices.

"Spintronics had traditionally dealt with thicker materials," Akiyama explained. "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."

The conversion mechanism, known as the circular photogalvanic effect (CPGE), aligns electron spins in one direction, restricting electrical current flow based on light polarization. Similar to how conventional diodes control current with voltage polarity, this effect relies on light-induced spin alignment. Using thallium-lead alloys, researchers conducted experiments in ultra-high vacuum conditions to prevent material degradation, revealing the unique electronic behavior of the alloys under circular polarized light.

Akiyama added, "Even more surprisingly, 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."

The team's prior work with thin alloys, which demonstrated unique electronic properties, inspired the current study. Looking ahead, Akiyama emphasized the importance of foundational research for practical applications, expressing interest in using terahertz lasers to refine excitation paths and enhance the efficiency of light-to-current conversion.

"These results show that basic research is crucial for applications and development," Akiyama said. "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."

Research Report:Surface Circular Photogalvanic Effect in Tl-Pb Monolayer Alloys on Si(111) with Giant Rashba Splitting