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New traffic rules in “Graphene City”

Topological control of electrons (depicted as blue and red cars) in the double-layered graph. Credit: Seana Wood / Penn State…



Topological control of electrons (depicted as blue and red cars) in the double-layered graph. Credit: Seana Wood / Penn State MRI

In the quest to find new ways to expand the electronics beyond the use of silicon, physicists experiment with other properties of electrons at no charge. In a work published today (7 Dec) in the journal Science a team led by Penn State Professor of Physics Jun Zhu describes a way of manipulating electrons based on their energy in relation to momentum called “Valley of Liberty . “

“Imagine that you are in a world where electrons are colored red or blue,” said Zhu, “and the routes that electrons travel on are also colored red or blue. Electrons may only travel on the same road, so that a blue electron would need to be a red electron to travel on the red road. “

Two years ago, Zhus showed that they could build color-coded two-way roads in a material called the double-sided graph. Due to their color coding, these roads are topological. In the current study, the researchers made a four-way crossing where the color coding of the roads was hit on the other side. Therefore, you have a situation where a blue car traveling north comes to this intersection and finds that on the other side the intersection is the northern roads colored red. If the electron can not change color, it is forbidden to travel forward.

These roads are actually electron waveguides created by gates defined with extreme precision using state-of-the-art electron beam lithography. The colors are actually the dale index of the cars, and the color coding of the road coding is controlled by the waveguide’s topology, which is analogous to the left-hand drive and right-hand drive rules in different countries. Changing the color of the cars requires “medium spread” minimized in the attempt to enable traffic control.

“What we have achieved here is a topological valley valve, which uses a new electron flow control mechanism,” said Zhu. “This is part of a flowing field of electronics called valleytronics. In our experiment, the topology controlled the deceleration of electrons &#821

1; which made it work.”

In the study, the researchers asked where was metaphorical blue car if it could not go on?

Dr. Jun Zhu, professor of physics, explains the wave leaders that her team creates in the 2D chart with an eye on expanding electronics beyond silicon. An animation of color-coded cars explains how electrons can be controlled through the waveguides with precision. Credit: Materials Research Institute, Penn State

“It must turn either left or right,” said senior author Jing Li, Zhu’s former doctoral student, now a director’s postdoc in Los Alamos National Lab.

“We have additional ways to control the twist traffic – by moving the track incrementally closer to right or left turn, the percentage of electrons / cars turning right or left can be easily adjusted to 60 percent in one way, 40 percent the other or some other combination of percentages. “

This controlled partition is called a beam splitter, which is common to light but not easily accomplished with electrons. Zhu and Li said they are happy about the control they have achieved for their color-coded paths, as it allows more advanced experiments on the road.

“The creation of the device requires many steps and quite complicated e-beam lithography,” said Li. “Thankfully, Penn State’s state-of-the-art nanofabrication facility and a team of professional support staff made it possible for us to do all of this.”

The next challenge for Zhus’s team is to try to build their units to work at room temperature instead of at the very cold temperatures they currently need. It is feasible, Zhu believes, but challenging.

“The approach we took to make the device is scalable,” said Zhu. “If large-scale double sided graph and hexagonal boron nitride becomes available, we can potentially make a city of topological roads and shuttle electronics to places they need to go, all without resistance. That would be very cool.”


Explore further:
Unit for controlling “color” of electrons in the graph gives way to future electronics

More information:
“A valley valve and electron beam splitter” Science (2018). science.sciencemag.org/cgi/doi … 1126 / science.aao5989

Journal Reference:
Science

Provided by:
Pennsylvania State University

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