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.
The device was built to explore fundamental physics and realize a previously unobserved behaviour, 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 device has the potential to turn into something that measures different aspects of light,” says lead researcher Yiming Gong, “but this originates from a very fundamental level of physics, which is the interference between different optical absorption processes.”
The researchers showed they could induce the orderly flow of electrons through a semiconductor using two different colours of light.
By rotating the polarisation of the two optical fields, 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 electric 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 researcher Steven Cundiff.
Although previous work had shown that light alone could get electrons flowing, this work goes a step further and shows that light gets electrons flowing in a narrow beam in a specific direction.
“The light no longer merely switches the current on; it also aims it,” Cundiff said..
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 quantised photons, which mobilise the material’s electric charge carriers.
In the U-M setup, the incident light is absorbed by two routes at once. They enhance each other for electrons traveling in the same direction but cancel each other out for electrons moving in other directions.