Scientists at the University of Michigan have successfully demonstrated a semiconductor device that uses laser light to control the directional flow of electrons through a material without requiring any applied electric field or external power source. The research was supported by the U.S. National Science Foundation and represents the first experimental realization of a theoretical concept that had been predicted but never previously achieved.
The device operates by utilizing two different colors of light to produce an organized electron current through the semiconductor material. Researchers discovered they could alter the direction of this electron flow by adjusting the polarization characteristics of the optical fields being used. The effect draws its name from the visual metaphor of a lighthouse beam, as the electron stream can be rotated and directed similarly to how a rotating lighthouse lamp sweeps its light across the horizon.
The underlying mechanism depends on quantum interference effects within the semiconductor material. When two colors of light interact with the semiconductor simultaneously, they create different absorption pathways that lead to the same final quantum state. This process is comparable to overlapping ripples in water, where the waves either reinforce or cancel each other depending on direction. For electrons moving in one direction, the interference patterns align and strengthen, while in other directions they cancel out, creating a concentrated current rather than a dispersed one.
The research team, led by physicist Steven Cundiff and doctoral student Yiming Gong, faced significant manufacturing challenges during the project. A critical aspect involved preventing unwanted electric fields from forming during the device’s fabrication, as confirming that electron movement resulted solely from light exposure was essential to validating the findings. The researchers collaborated with the Lurie Nanofabrication Facility to develop novel manufacturing processes and test various fabrication methods.
While the device was primarily created to explore fundamental physics principles, the discovery has potential applications in technologies combining optics and electronics, such as advanced sensing systems, imaging technologies, and telecommunications infrastructure. The research findings were published in the journal Physical Review Letters.
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