When two pulses of different colored lasers (the two waves at the top of the image) light meet in a new device created at the University of Michigan, researchers create a beam of electrons (small golden particles) that flows in a controllable direction. By changing the laser colors, the electron beam can sweep through different directions like the beam of a lighthouse.
Image Credit: Yiming Gong
Scientific Frontline: Extended "At a Glance" Summary: Electron Lighthouse
The Core Concept: A newly developed semiconductor device utilizes two distinct colors of phase-coherent laser light to generate and precisely steer a directional flow of electrons without relying on an external electrical power source.
Key Distinction/Mechanism: Traditional electrical currents rely on an applied electric field that causes electrons to randomly bounce and drift through a material. In contrast, this device uses quantum interference—where two colors of light drive different absorption pathways to the same final state. These optical pathways overlap like ripples, amplifying electron movement in a chosen direction while canceling out movement in others. By rotating the polarization of the optical fields, researchers can aim the narrow electron beam much like a lighthouse sweeping its light.
Major Frameworks/Components:
- Quantum interference governing multiple optical absorption processes.
- Phase-coherent optical fields and polarization manipulation.
- Photoexcitation of electric charge carriers within semiconductor materials using quantized photons.
- Directional photocurrent generation operating independently of external voltage.
Branch of Science: Quantum physics, optoelectronics, optics, and solid-state physics.
Future Application: This technology could serve as the foundation for advanced devices in precision sensing, optical imaging, telecommunications, and new methodologies for storing denser information within optical signals.
Why It Matters: The project demonstrates a previously unobserved fundamental physical behavior, successfully bridging optics and electronics. By proving that light can not only mobilize electrons but also precisely aim their trajectory, it expands both the theoretical understanding and practical control of electronic currents.
Researchers at the University of Michigan have created a device that enables them to control the flow of electrons through a semiconductor using only laser light—no electrical power source required.
This device was built to explore fundamental physics and realize a previously unobserved behavior, but it could also open doors for new applications in areas that bridge optics and electronics, including sensing, imaging, and telecommunications. The phenomenon could help improve how signals are sent through and between devices, as well as create new opportunities to store more information in those signals.
“This electrical device that we manufactured at the Lurie Nanofabrication Facility has the potential to turn into something that measures different aspects of light,” said Yiming Gong, who helped lead the project as a doctoral student in the U-M Department of Physics. “But this originates from a very fundamental level of physics, which is the interference between different optical absorption processes.”
With federal support from the U.S. National Science Foundation, the researchers showed they could induce the orderly flow of electrons through a semiconductor using two different colors of light. By rotating the polarization of the two optical fields—the direction in which the light waves oscillate—the researchers could also control the direction of the electronic current.
“This isn’t the way things normally work. When you think about electrons moving through a material, they’re moving because you’ve applied an electrical field and they actually bounce around and drift across the materials. Here, using light, you can actually sort of squirt the electrons in a specific direction without applying an electric field,” said U-M physicist Steven Cundiff, senior author of the team’s new report in the journal Physical Review Letters.
Although previous work had shown that light alone could induce electron flow, this study goes a step further, demonstrating that light can direct electrons in a narrow beam toward a specific direction.
“The light no longer merely switches the current on; it also aims it,” Cundiff said.
Cundiff likens this to a lighthouse, which sweeps a beam of light by rotating its lamp. Here, the beam consists of electrons, and that beam can be directed by rotating the polarization of the two phase-coherent optical fields.
The phenomenon relies on quantum interference, which arises when two colors of light drive different absorption pathways to the same final state. The light transfers energy to the semiconductor material in discrete, or quantized, packets called photons, which mobilize the material’s electric charge carriers.
In the U-M setup, the incident light is absorbed by two routes at once, and the routes can be thought of as overlapping ripples, Cundiff said. Those ripples line up and enhance each other for electrons traveling in a certain direction, but they cancel each other out for electrons moving in other directions.
A collaborator on an earlier project, J. E. Sipe of the University of Toronto, had predicted it would be possible to create such an “electron lighthouse.” Now, working with the Lurie Nanofabrication Facility, Gong was able to realize such a device.
“The LNF is an amazing facility,” Gong said, adding that it was a painstaking process to meld the device’s materials together in a way that didn’t introduce any extraneous electric fields.
“That was the biggest puzzle to solve for me, because there isn’t a standard way to do that. So, I worked with the LNF staff to play around with different recipes and temperatures to come up with a manufacturing process.”
Funding: National Science Foundation
Published in journal: Physical Review Letters
Title: Directional Photocurrent Generated by Quantum Interference Control
Authors: Yiming Gong, Kai Wang, and Steven T. Cundiff
Source/Credit: University of Michigan
Edited by: Scientific Frontline
Reference Number: qs072126_01
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