By Josh Perry, Editor
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Researchers from Penn State University (University Park, Pa.) have developed a method for controlling electrons in bilayer graphene by manipulating them based on their relation to momentum (called the valley degree of freedom), creating electronic roadways for the electrons to travel.

Topological control of electrons (depicted as blue and red cars) in bilayer graphene.
(Seana Wood/Penn State MRI)

Previous research efforts demonstrated that color-coded topological “roads” could be created for electrons to follow, according to a report from the university. So, “blue” electrons could only travel down blue roads and “red” electrons had to stay on the red road.

Now, researchers have developed a four-way intersection with the color-coded roads changing on the opposite side. A blue electron traveling in one direction would have to change switch color in order to continue to the other side. 

“These roads are actually electron waveguides created by gates defined with extreme precision using state-of-the-art electron beam lithography,” the article explained. “The colors are actually the valley index of the cars, and the color-coding of the roads is controlled by the topology of the waveguides, analogous to the left-driving and right-driving rules of different countries. Changing the color of the cars requires ‘inter-valley scattering,’ which is minimized in the experiment to enable the traffic control to work.”

Obviously, for the color-coded electrons to continue on, they need to turn left or right. The percentage of electrons that turn in either direction can be tuned using a beam splitter that creates a partition directing the electrons.

This experiment requires extreme cold and researchers are working on being able to perform studies at room temperature.

The research was recently published in Science. The abstract stated:

“Developing alternative paradigms of electronics beyond silicon technology requires the exploration of fundamentally new physical mechanisms, such as the valley-specific phenomena in hexagonal two-dimensional materials.

“We realize ballistic valley Hall kink states in bilayer graphene and demonstrate gate-controlled current transmission in a four-kink router device. The operations of a waveguide, a valve, and a tunable electron beam splitter are demonstrated. The valley valve exploits the valley-momentum locking of the kink states and reaches an on/off ratio of 8 at zero magnetic field.

“A magnetic field enables a full-range tunable coherent beam splitter. These results pave a path to building a scalable, coherent quantum transportation network based on the kink states.”

Learn more from researchers in the video below: