A hero sandwich of many ultrathin layers allows superconductors to act as transistors.

Superconductors Poised to Make Circuits

Electronic devices are ruled by semiconductors such as silicon, but superconductors--metals and ceramics that conduct electricity without building up heat--are poised to make a power grab. Researchers have created the first superconducting device that behaves like a transistor, an achievement that could provide the electronic circuitry for specialized telescope sensors and other low-temperature gadgets.

A standard transistor is basically a switch. A small electrical voltage applied to one electrode--called the "gate"--increases the electrical conductivity between two other electrodes, allowing a large current to flow from one to the other. This "gain" in current prevents signals from decaying as they travel, and that's a key reason why transistors are crucial for the complex circuits of electronics. But resistance builds up heat inside these devices and limits how tightly circuits can be packed. A superconducting transistor, in contrast, wouldn't give off heat or lose current.

A team led by physicists Norman Booth of the University of Oxford, United Kingdom, and Antonio Barone of the University of Naples, Italy, have constructed such a transistor out of ultrathin layers of superconductors, insulators, and normal metals. Here's how it works: A few electrons are constantly hopping from the first superconductor, crossing an insulating layer into a second superconductor and then into a layer of aluminum, a nonsuperconducting metal. They stop right there. To flip the switch, a small voltage is applied to a third superconducting layer. This gives electrons in the aluminum enough energy to stream from the second to third superconductor, producing an impressive 70-fold gain over the amount of current injected into the first superconducting layer, the team reports in the 17 July issue of Applied Physics Letters.

Superconducting electronics could be a boon to efforts to build the world's first petaflop computer--capable of one thousand trillion floating point operations per second--says superconductivity expert John Rowell of Northwestern University in Evanston, Illinois. But Booth adds that the first applications will likely come in electronics for telescopes and other devices operating near absolute zero, a world where conventional electronics falter.

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Applied Physics Letters