Valleytronics …

A device made of bi layer graphene, an atomically thin hexagonal arrangement of carbon atoms ,provides experimental proof of the ability to control the momentum of electrons and offers a path to electronics that could require less energy and give off less heat than standard CMOS transistors.  It is one step forward in a new field of physics called valleytronics.

Current silicon based transistor device rely on the charge of electrons to turn the device on or off ,but many labs are looking at new ways to manipulate electrons based on other variables, called degree of freedom. Charge is one degree of freedom . Electron spin is another and the ability to build transistors based on spin called sprintronics ,is still in the development stage . A third electronic degree of freedom is the valley state of electrons which is based on their energy in relation to their momentum.

Think of electrons as cars and the valley States as red and blue colors ,just as a way to differentiate them. Inside a sheet of bilayer graphene, electrons will normally occupy both red and blue valley States and travel in all directions.

The device on which the scientists are working can make the red cars go in one direction and blue cars in the opposite direction . The system that is created puts a pair of gates above and below a bi layer graphene sheet . Then adds an electric field perpendicular to the plane .

By applying a positive voltage on one side and a negative voltage on the other , a band gap opens in bilayer graphene, which it doesn’t normally have . In the middle , between the two sides we leave a physical gap of about 70 nanometers.

Inside this gap lives one dimensional metallic states or wires that are colour coded freeways for electrons. The red cars travels in one direction and the blue cars travel in the opposite direction. In theory , coloured electrons could travel unhindered along the wires for a long distance with very little resistance.  Smaller resistance means power consumption is lower in electronic devices and less heat is generated . Both power consumption and thermal management are challenges in current miniaturized devices.

It’s quite remarkable that such sites can be created in the interior of an insulating bilayer graphene sheet, using just a few gates. They are not yet resistance free and we are doing more experiments to understand where resistance might come from . We are also trying to build valves that control the electrons flow based on the colour of the electrons . That’s a new concept of electronics called volleytronics.

  • Navyashree

 

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