How do we store information? One way is to use a magnetic media, like as is done in our hard drive, where the information is encoded into the total magnetization of a group of spins. Another way is to use a capacitor and transistor to store information into the charge on the capacitor.
Now researchers at Philips Research Laboratories in Eindhoven, the Netherlands ( Lankhorst M. H. R., Ketelaars B. W. S. M. M. & Walkters R. A. M. Nature Materials published online, doi: 10.1038/nmat1350 (1968)) have created a storage medium in which the information is stored in a very strange way. Instead of the information being encoded into the total charge or the magnetization, their information is encoded into the degree of freedom describing whether the media they have is ordered or disordered. The idea of storing information in the ordered versus disordered phase has been around for a long time (such devices are called “Ovonic”) but apparently this new research is the first really viable realization of such a device.
The researchers use antimony telluride, which is naturally in an amorphus state with many of the atoms of the material all jumbled around. A small electral pulse however, will turn this state into an ordered states with the atoms lined up in a crystaline structure. A larger electral pulse (more voltage), however, will melt this crystaline structure and return the system into the disordered jumble of atoms. The state of the system can be read out by measuring the resistance across the material (the ordered phase will have a much lower resistance.) Thus we can store our binary 0 in the ordered phase and our binary 1 in the disordered phase, read out this information, and also write this information.
Which makes me wonder which other order parameters in statistical physics can be used to store information? Can we store information in the two phases of a metal being superconducting and just regularly conducting? How about in fluid-superfluid transition? OK, both of these are totally not practical, but maybe there is an interesting order parameter which we are missing but which would make an amazingly robust and fast storage device?
O brave new quantum world!
Here is a room with more than a bit of information!
How is this different from phase change optical storage media? Those have been in production for years; a laser heats a material and changes between crystalline and amorphous, which changes the reflectivity. The material is some complex of metals and semiconductors…
(Thanks to Ben Kobler for pointing this out.)
Good point!
I guess what’s interesting here then is not that it is transitioning between ordered and disordered, but that these changes change the electral properties of the substance (alothough reflectivity is essentially an electral property, no?) and are switched by electral voltages. I guess that’s the main new feature: switched by voltages. And I think the speed is better than that of optical storage media.