エレクトロニクスは、電子の電荷の自由度を、スピントロニクスが電子のスピンの自由度を、そして、バレートロニクスは電子のバレー自由度を利用しているそうです。そもそもバレーとは何なのか?という話で、valleytronicsのvalleyとは、conduction band minima(伝導バンドの極小)かvalence band maxima(価電子帯の極大)点付近に形成されるバンドのことのようです。バレートロニクスが今熱いテクノロジーのようです。



A device made of bilayer 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 silicon-based transistors. It is one step forward in a new field of physics called valleytronics.




“Current silicon-based transistor devices 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 degrees of freedom,”


“Charge is one degree of freedom. Electron spin is another, and the ability to build transistors based on spin, called spintronics, 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 blue and red colors, Zhu suggested, 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 her Ph.D. student, Jing Li, has been working on can make the red cars go in one direction and the blue cars in the opposite direction.

「単にそれらを差別化する手段として、電子を車に、バレー状態を青と赤として考えてみて下さい、とZhuは言いました。2層グラフェンのシートの内部で、電子は普通に赤と青のバレー状態の両方を専有し、四方八方に移動しています。彼女の博士課程生徒のJing Liが研究しているデバイスは、赤い車を1方向へ、青い車を反対方向に向かわせる事ができます。」

“The system that Jing created puts a pair of gates above and below a bilayer graphene sheet. Then he adds an electric field perpendicular to the plane,”


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




Inside this gap live one-dimensional metallic states, or wires, that are color-coded freeways for electrons. The red cars travel in one direction and the blue cars travel in the opposite direction. In theory, colored 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.



“Our experiments show that the metallic wires can be created,” Li said. “Although we are still a long way from applications.”



“It’s quite remarkable that such states 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 electron flow based on the color of the electrons. That’s a new concept of electronics called valleytronics.”