SUPERCONDUCTIVITY is usually turned on and off by cooling a material and then warming it up again. Now this switching has been done electronically, an achievement that could lead to far faster computer chips.
When certain metals are cooled to within a few degrees of absolute zero, quantum effects cause electrons to stop repelling each other and pair up. It is this pairing up that leads to superconductivity, the total absence of any electrical resistance.
Superconductors are an attractive future alternative to the microscopic semiconductor switches that are the ultimate building blocks of computer chips, as their lack of resistance means they can function much faster and do not generate any waste heat. They have not so far been widely used as a replacement for silicon because they are very difficult to fabricate and manipulate.
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Now Kei Takahashi and colleagues at the University of Geneva in Switzerland have taken a big step forward by showing it is possible to switch a superconductor on and off electronically. The researchers coated a thin film of superconductor with a layer of ferroelectric 鈥� a material with a small internal electric field. Using the needle of an atomic force microscope (AFM), they then altered the direction of the electric field at specific points in the ferroelectric, which in turn changed the density of electrons in the underlying superconductor. As superconducting behaviour only occurs at certain electron densities, this turned the electrical resistance on and off in different parts of the film (Nature, vol 441, p 195).
The discovery opens up a broad avenue of research into faster computer chips, says team member Jean-Marc Triscone. AFMs could even act as superfine pens to draw circuits or device patterns onto the ferroelectric, which would then be electronically imprinted in the superconductor layer. The ability to use AFMs to control properties and create structures at the nanoscale level could be used to create ever smaller chips and circuits, says team member Mikk Lippmaa at the University of Tokyo.
鈥淎tomic force microscopes could act as superfine pens to draw circuits or patterns鈥�
Practical applications look a long way off, however, as the superconductor switch only operates within about a degree of absolute zero. The researchers now plan to investigate more complex circuits and other materials that stay superconductive at higher temperatures.
