快猫短视频

ELECTRON spin may be the solution computer-chip makers have been looking for
in their struggle to squeeze ever smaller and faster devices onto their
chips.

Exploiting the intrinsic 鈥渟pin鈥� of electrons will provide a wealth of
possibilities, and scientists have taken a key step in this direction,
developing a battery that can store electron spin and release it on demand.

Today鈥檚 electronic devices work by shuffling packets of electric charge
around a semiconductor circuit, in the form of groups of electrons. But
electrons also spin, giving them a magnetic field like a tiny bar magnet.

If you align the spin axes of all the electrons in a group鈥攌nown as
spin polarisation鈥攖hen the group has another property that you can use to
carry information. The 鈥渟pin-up鈥� or 鈥渟pin-down鈥� state can correspond to the 0s
and 1s of digital code. Circuits that exploit this property are known as
鈥渟辫颈苍迟谤辞苍颈肠蝉鈥�.

Manipulating spin is fairly easy in magnetic metals because the spins line up
naturally along the metal鈥檚 field. But controlling spin in semiconductors has
proved difficult.

Now, a team led by David Awschalom from the University of California at Santa
Barbara has shown that they can store and control spin-polarised electrons in a
layered semiconductor material.

The spin battery is made up of one layer of gallium arsenide and one of zinc
selenide. The researchers polarise spin in the gallium arsenide layer using
pulses of circularly polarised light. Normally, an energy barrier between the
two layers prevents most of the electrons crossing into the zinc selenide. But
the researchers found that they could release the electrons at will without
destroying their spin polarisation, by applying an electric field across the
junction.

Michael Flatte of the University of Iowa in Iowa City says the stability of
the spin polarisation surprised him. 鈥淭hat is something that was really not
expected,鈥� he says.

Controlling the flow of spin-polarised electrons paves the way for building
devices such as 鈥渟pin transistors鈥�, which could combine current amplification
with the ability to remember data when the power is turned off. One of the most
exciting possible applications is in quantum computers, which will use the
quantum uncertainty of electron spins to process data at superfast speeds.

But Awschalom thinks the best uses have yet to be dreamed up. 鈥淭he most
exciting aspects are the ones we are not yet thinking about,鈥� he says.