Light controlling electron flow on a crystal surface

Spin Control: How Light Could Revolutionize Electronics

Samir D’Costa in Tech & Innovation August 2025 • 4 min read.

"New research unveils how manipulating light polarization can precisely control spin-polarized photocurrents in topological insulators, paving the way for advanced optoelectronic and spintronic devices."

For years, scientists have been captivated by the potential of topological insulators (TIs)—materials that act as insulators on the inside but conduct electricity flawlessly on their surface. What makes them even more intriguing is the spin of their electrons is locked to their momentum, a property known as spin-momentum locking. This unique characteristic has opened doors to controlling photocurrents and spin currents without needing external fields, promising a new era of electronics.

However, working with TI crystals that have electrodes presents a significant challenge. The coexistence of surface and bulk carriers generated by light makes it difficult to isolate and study the net flow of spin-polarized photocurrents. This is where a groundbreaking study comes into play, offering a way to precisely and intentionally control the flow directions of these photocurrents in TI polycrystalline thin films without electrodes.

Researchers have demonstrated that by carefully manipulating the polarization of excitation pulses, they can direct the net flow of spin-polarized photocurrents. This innovative approach, characterized by time-domain terahertz (THz) wave measurements and time-resolved magneto-optical Kerr rotation measurements (both non-contact methods), could revolutionize optoelectronic and spintronic devices.

How Does Light Control Electron Flow?

Light controlling electron flow on a crystal surface

The study focused on using light to induce and control electrical currents within topological insulators. When light shines on these materials, it excites electrons, causing them to move and create a current. The key is that the direction of this current can be controlled by adjusting the polarization of the light—specifically, whether the light is polarized circularly to the right or the left. This is crucial for applications where you want to guide the flow of electrons very precisely.

To visualize this control, imagine you're directing traffic with a flashlight. By twisting the flashlight's lens (adjusting the light's polarization), you can change the direction cars (electrons) move. The key findings include:

Inverted THz Waves: The direction of terahertz waves (a form of electromagnetic radiation) emitted by the photocurrents flips when switching between right and left circularly polarized light. This directly shows that the direction of the current is reversed.
Kerr Rotation Inversion: Measurements of magneto-optical Kerr rotation, which is sensitive to the spin polarization of the electrons, also show an inversion when the light polarization is switched. This confirms that not only the direction but also the spin of the electrons is being controlled.
No Electrodes Needed: The experiment was conducted without electrodes, meaning the control is purely optical, reducing the complexity of devices and opening new possibilities for wireless control.

These results are pivotal because they demonstrate a method to manipulate spin-polarized electrons in optoelectronic and spintronic TI devices without needing external fields. This simplifies device design and enhances efficiency by minimizing external interference. By understanding and harnessing this level of control, we are one step closer to creating devices that use light to perform complex operations with unprecedented speed and precision.

The Future of Electronics is Light?

This research paves the way for innovative methods to control spin-polarized electrons in optoelectronic and spintronic TI devices, potentially leading to faster, more energy-efficient electronics. The ability to manipulate electron flow with light could revolutionize various applications, from high-speed computing to quantum information processing. As the field progresses, we can anticipate seeing these principles integrated into next-generation devices that leverage the unique properties of topological insulators.

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Everything You Need To Know

What are topological insulators and why are they important for new electronics?

Topological insulators (TIs) are materials that act as insulators on the inside but conduct electricity flawlessly on their surface. They are important because of their unique property called spin-momentum locking, where the spin of their electrons is locked to their momentum. This allows for the control of photocurrents and spin currents without needing external fields, which is a key enabler for faster and more efficient electronics. This is a foundational aspect of creating devices that can perform complex operations with unprecedented speed and precision.

How does light polarization control electron flow in topological insulators?

Light polarization is used to control electron flow by manipulating the direction of the net flow of spin-polarized photocurrents within the topological insulators. The study focused on using light to induce and control electrical currents within topological insulators. By adjusting the polarization of the light—specifically, whether the light is polarized circularly to the right or the left—researchers can control the direction of the current. The direction of terahertz waves, emitted by the photocurrents, flips when switching between right and left circularly polarized light, showing that the current direction reverses. Measurements of magneto-optical Kerr rotation also invert with the light polarization change, confirming that both the direction and spin of the electrons are controlled.

What are the key findings of the study and how do they impact the development of new electronic devices?

The key findings include the inversion of terahertz (THz) waves and Kerr rotation when switching between right and left circularly polarized light. The experiment was also conducted without electrodes. These results demonstrate a method to manipulate spin-polarized electrons in optoelectronic and spintronic topological insulator (TI) devices without needing external fields. This simplifies device design and enhances efficiency by minimizing external interference. This opens doors for innovative methods to control spin-polarized electrons in optoelectronic and spintronic TI devices, potentially leading to faster, more energy-efficient electronics.

What are the implications of using light to control electron flow in electronic devices, as demonstrated by the study?

The ability to manipulate electron flow with light could revolutionize various applications, from high-speed computing to quantum information processing. The implications include the potential for faster and more energy-efficient electronics because light offers a non-contact, highly precise method to control electron flow. This could lead to the development of wireless control systems, more compact devices, and advancements in quantum computing, where precise control of electron spin is critical. This technology simplifies device design, minimizes interference, and opens up new possibilities for electronic device functionality.

How do time-domain terahertz (THz) wave measurements and time-resolved magneto-optical Kerr rotation measurements contribute to the study's findings?

Time-domain terahertz (THz) wave measurements and time-resolved magneto-optical Kerr rotation measurements are non-contact methods used to confirm and analyze the control of electron flow. The THz wave measurements are used to determine the direction of the current. When the polarization of the light is switched, the direction of the THz waves emitted by the photocurrents flips. The magneto-optical Kerr rotation measurements reveal information about the spin polarization of the electrons, confirming that not only the direction but also the spin of the electrons is being controlled by light polarization. Together, these measurements provide strong evidence that light polarization can be used to precisely control and manipulate spin-polarized photocurrents in topological insulators (TIs), paving the way for advanced optoelectronic and spintronic devices.