Crave Talk: Spin's the thing for future gizmos
An ancient Swedish chemist, anti-social rats and deep quantum weirdness all have their roles to play in 21st-century electronics. But first, let us take you back to the pressing problems of Elizabethan England...
Blackadder II; Episode 4. Things are looking bad for Lord Blackadder. In 12 hours the baby-eating Bishop of Bath and Wells is to kill him over a debt, and all his schemes have come to nothing. Enter Lord Percy, with the answer:
Lord Percy: After literally an hour's ceaseless searching, I have succeeded in creating gold, pure gold.
Blackadder: Are you sure?
Lord Percy: Yes, my lord. Behold.
Blackadder: Percy... it's green.
Lord Percy: That's right, my lord.
Blackadder: Yes, Percy, I don't want to be pedantic or anything, but the colour of gold is gold. That's why it's called gold. What you have discovered, if it has a name, is 'green'.
Lord Percy: Oh, Edmund, can it be true, that I hold here in my mortal hand a nugget of purest green?
Blackadder: Indeed you do, Percy, except, of course, it's not really a nugget, it's more of a splat.
Lord Percy: Well, yes, a splat today... but tomorrow -- who knows, or dares to dream?
As always, deep within television comedy great scientific truth can be found. The real Lord Percy was the 18th-century Swedish chemist Sven Rinmann, who also spent his days mucking around with gunk. His great discovery was cobalt green, which was remarkable for two reasons -- it was a nice translucent shade so was attractive to artists; and rather expensive, therefore out of their reach. And that's been that.
Until now. Researchers at the University of Washington have found that cobalt green does strange things to the electrons inside it. Under the influence of other electrons, they can line up in odd ways -- and stay lined up. This could be the key to a brand new sort of computer chip. This technology, known as spintronics, may let us carry on inventing, even as traditional silicon chips run out of steam.
Spintronics might sound like an 80s electro-rock band, but it's funkier than that. Everything we do with the digital is courtesy of armies of electrons -- the sub-atomic particles we've enslaved and bent to our will. Electrons don't like each other -- they all have a negative charge and therefore repel. We've learned how to make small numbers of electrons control larger numbers through that mutual repulsion; they skitter around circuits trying to avoid each other like anti-social rats in a maze. Design the maze to reflect simple rules -- if there's a rat to your right, turn left, otherwise keep going -- and you can build processors, chipsets, iPods, the Internet and Big Brother on hi-def TV.
But that's only using half the electron's superpowers. Electrons don't just have a charge, they also have spin. They don't really spin, but the idea is a convenient shorthand for deeply weird quantum behaviour, which only makes sense to people who don't make sense to anyone else.
You already use electron spin in your computer's hard disk. Like tape recorders, a hard disk stores its information as a magnetic pattern written by a recording head: pulse some electricity through that head, and the disk platter or tape beneath it picks up and stores the resulting magnetic pattern. The north-south magnetic alignment depends on which way the electrons spin, and vice-versa. Flip the spin and you flip the magnet.
Because the electrons are locked in place and spin doesn't wear out, magnetic patterns are a really good way to store information for a long time -- indeed, we can still read the Earth's magnetic field by the magnetic patterns in rocks laid down hundreds of millions of years ago. Now there's reliable data storage for you! Unfortunately it takes a lot of power to flip the spin of electrons and mechanically reading the information back through rotating disks and moving heads is slow, so that kind of storage isn't any good for fast computing. That's why you've also got silicon memory in your computer.
Silicon is a really good way to get information in and out of computers fast. That works by electrons too, but by using their charge to move them in and out of storage bins. The problem is that you can never seal off the storage bins perfectly. Like rats through a hole, the electrons escape. Turn the power off, and the data's lost. And while you can make silicon memory really fast, every time you move electrons you waste energy; and the faster you move them, the more energy you use.
You don't move an electron when you change its spin, so that could be both very fast and much more energy efficient, and you can lock the electrons into permanent stores that last forever. So far, there's been no way to influence or read spin other than by boringly mechanical contraptions -- we haven't been able to build purely electronic devices that handle it. Or rather we have, but they're fragile and unreliable things that need to be cooled to cryogenic temperatures -- not much use for an iPod.
Which is where we get back to Lord Percy. Within the lattice of cobalt and zinc atoms in cobalt green, the electrons can be made to align their spins purely by the influence of other electrons -- and then keep that spin once the other electrons go away. What's more, it happens at room temperature.
If we can find out how that works and then build it into silicon chips, we could make the perfect memory that works screamingly fast, remembers stuff forever with no power, and needs only a few atoms per bit. It could even lead to faster, smaller, ultra-low power processors that run rings around current electronics. We won't be able to do this for at least ten years, although coincidentally, that will be around the time when ordinary silicon engineering is expected to start to running out of options. Now there's a cunning plan. -Rupert Goodwins