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New traffic rules in ‘Graphene City’



Topological control of electrons (shown as blue and red cars) in double-layer graphene. Credit: Seana Wood / Penn State MRI

In an effort to find new ways to extend electronics beyond the use of silicon, physicists are experimenting with other properties of electrons, beyond charge. In the paper published today (December 7) in the journal Science a group led by physics professor Penn State, Jun Zhu describes a way to manipulate electrons based on their energy in relation to the "valley level" the freedom."

"Imagine you are in a world where the electrons are colored, red or blue," said Zhu, "and even the roads on which the electrons travel are colored red or blue. The electrons can only travel on roads of the same color, so that a blue electron would turn into a red electron to travel on the red road. "

Two years ago, Zhu's team showed that they could build two-way color-coded roads in a material called double-layer graphene . Because of their color coding, these roads are topological. In the present study, the researchers realized a four-way intersection in which the color coding of the streets is activated from the other side. Therefore, you have a situation where a blue car traveling north arrives at this intersection and discovers that from the other side of the intersection the roads in the north direction are colored red. If the electron can not change color, it is forbidden to travel forward.

These streets are actually electronic wave guides created by precisely defined doors using electron beam lithography in the state of art. The colors are actually the index of the car valley, and the color coding of the streets is controlled by the topology of the wave guides, similar to the rules of left-hand drive and right-hand drive of the different countries. Changing the color of cars requires "scattering between the valleys", which is minimized in the experiment to allow traffic control to work.

"What we have achieved here is a topological valve, which uses a new mechanism to control the flow of electrons," Zhu said. "This is part of an electronics testing field called Valleytronics. In our experiment, topology control ̵

1; blocking the moment of the electron valley – is what made it work."

In the study, researchers asked where the metaphoric blue car would be if they could not travel ahead




Dr. Jun Zhu, professor of physics, explains the wave guides that his team creates in 2D graphene with an eye on the expansion of electronics beyond silicon. A color-coded car animation explains how electrons can be directed through the precision waveforms. Credit: Materials Research Institute, Penn State

"It will have to turn right or left," said lead author Jing Li, a former Ph.D. student at Zhu, now a post-doctoral fellow at Los Alamos National Lab. [19659005] "We have additional ways to control turn traffic, moving the lane incrementally closer to a right or left turn, the percentage of electrons / cars turning right or left can be adjusted evenly to get 60 percent in one way, 40 percent or any other combination of percentages. "

This controlled partition is called a" beam splitter ", which is common for light but is not readily achievable with electrons. Zhu and Li said they were enthusiastic about this control they achieved on their color-coded roads, since it allows more advanced experiments along the way.

"The creation of the device requires many steps and quite complicated electron beam lithography," Li said. "Fortunately, Penn State's nanofabrication facility at the cutting edge and a team of professional support staff have enabled us to do all of this."

The next challenge for the Zhu team will be to try to build their devices to operate at room temperature rather than the very cold temperatures they currently need. It's feasible, Zhu believes, but it's a challenge.

"The approach we took to make this device is scalable," Zhu said. "If double-layer graphene and hexagonal boron nitride become available, we can potentially build a city of topological streets and shuttle electrons in places where they have to go, all without resistance.


Explore further:
The device to control the "color" of electrons in graphene provides the path to future electronics

Further information:
"Downstream Valve and Electron Beam Splitter" Science (2018). science.sciencemag.org/cgi/doi … 1126 / science.aao5989

Journal reference:
Science

Provided by:
State University of Pennsylvania


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