Faster computer clock speeds on the way?

In collaboration with researchers at the University of Augsburg in Germany, MIT Professor of Physics, Raymond Ashoori set out to investigate the unusual physical system that results when lanthanum aluminate is grown on top of strontium titanate. "Lanthanum aluminate consists of alternating layers of lanthanum oxide and aluminum oxide," he explained. "The lanthanum based layers have a slight positive charge; the aluminum based layers, a slight negative charge. The result is a series of electric fields that all add up in the same direction, creating an electric potential between the top and bottom of the material." The team of researchers found that both lanthanum aluminate and strontium titanate were excellent insulators as they didn't conduct electrical current. However, the physicists speculated that if the lanthanum aluminate got thick enough, its electrical potential would increase to the point that some electrons would have to move from the top of the material to the bottom, to prevent what's called a 'polarisation catastrophe'. The result was a conductive channel at the juncture with the strontium titanate, much like the one that forms when a transistor is switched on. As such, Ashoori and his collaborators decided to measure the capacitance between that channel and a gate electrode on top of the lanthanum aluminate. "We were amazed by what we found," said Ashoori. "Although our results were somewhat limited by our experimental apparatus, it may be that an infinitesimal change in voltage will cause a large amount of charge to enter the channel between the two materials. The channel may suck in charge like a vacuum, and it operates at room temperature, which is the thing that really stunned us." Indeed, the material's capacitance was so high that the researchers were not sure it could be explained by existing physics. "We've seen the same kind of thing in semiconductors," Ashoori noted, "but that was a very pure sample and the effect was very small. This is a super dirty sample and a super big effect. It's still not clear, however, just why the effect was so big. It could be a new quantum mechanical effect or some unknown physics of the material." While the researchers found that a lot of charge moved into the channel between the materials with a slight change in voltage, they realised that it moved much too slowly for the type of high frequency switching that takes place in computer chips. "This is not going to revolutionise electronics tomorrow," Ashoori asserted, "but this mechanism exists, and once we know it exists, if we can understand what it is, we can try to engineer it."