Korean researchers induce magnetism in non-magnetic semiconductor using light

Korean researchers have developed a technique that momentarily generates magnetism in a non-magnetic semiconductor simply by shining light on it.

The Gwangju Institute of Science and Technology (GIST) said Monday that a joint research team led by Shin Dong-bin, a professor in its Department of Physics and Photon Science, and Kim Dong-eon, a professor in POSTECH's Department of Physics, successfully induced temporary magnetism in a two-dimensional non-magnetic semiconductor using light and identified the underlying mechanism.

Electrons carry a property called "spin," which causes them to behave like tiny magnets. By treating the direction of spin as the 0s and 1s of digital information, it is possible to build information-processing devices that are faster and consume less power than conventional semiconductors.

The research team confirmed that magnetism can be generated using only linearly polarized light — light whose electric field oscillates in a single direction.

The team fabricated single-layer and bilayer samples of molybdenum diselenide (MoSe₂), a two-dimensional semiconductor composed of molybdenum and selenium, and illuminated each with light.

No magnetic signal appeared in the single-layer sample, but in the bilayer sample the team clearly observed a rotation in the polarization of light — a signature of magnetism having formed.

The team found that this phenomenon arises from the coupling of two distinct types of atomic vibration.

An "interlayer breathing mode," in which the two layers alternately move toward and away from each other, and a "stretching mode," in which selenium atoms within each layer oscillate, occur simultaneously, driving the atoms into a complex combined motion.

In the process, an effect equivalent to applying a magnetic field to the electrons' spins emerges, giving rise to temporary magnetism.

Experiments confirmed both the interlayer breathing mode at 0.9 THz and the selenium stretching mode at 5.1 THz — exactly as theoretically predicted.

The team also analyzed how the magnetic signal varies with light intensity, photon energy and temperature.

The signal grew stronger as light intensity increased and peaked at around 1.55 electron volts (eV). At room temperature, the magnetic signal persisted for tens of picoseconds — one picosecond being one trillionth of a second — after the light was applied.

The findings are significant because they demonstrate that magnetism can be generated through light and atomic vibrations even in semiconductors that do not naturally possess it.

The technique could potentially be applied to ultrafast magnetic memory chips that control information with light rather than an external magnetic field, as well as to spintronics, valleytronics and quantum information devices.

The magnetism achieved so far, however, is a transient state lasting only tens of picoseconds. Further research will be needed to increase the strength of the magnetic signal and to sustain and control it stably before the approach can be applied to practical information-processing devices.

"This research confirms that atomic vibrations triggered by light, and the interactions between layers, play a crucial role in inducing magnetism," Shin said. "It is significant in showing that light and the spin of matter can be connected through atomic vibrations as an intermediary."

"We have experimentally verified in a real bilayer semiconductor the light-induced magnetism that was theoretically predicted," Kim said. "We hope this serves as a springboard for expanding research into controlling the magnetic properties of materials using light and atomic vibrations."

The findings were published in the online edition of Nature Communications on Oct. 5.