Aluminum "superatoms" hint at a new type of superconducting materials
Scientists at the University of Southern California (USC) have made steps toward discovering a new family of superconductor materials that work at relatively high temperatures, with possible applications in physics research, medical imaging and high-performance electronics.
As electrons travel through an integrated circuit, they regularly bump into microscopic imperfections within the conductive wire and veer off course, creating electrical resistance and releasing waste energy as heat. Waste heat is a big inconvenience to both designers and end-users of electronics, but it simply can’t be avoided using the materials currently at our disposal.
Superconductors can carry electricity with no resistance and are used for specialized applications like MRIs, maglev trains and particle accelerators. Superconductor-based electronics would be extremely efficient because they would generate no waste heat, but he fact that they would only work at temperatures close to absolute zero makes them impractical. Thirty years ago, a new class of so-called "high-temperature superconductors" was discovered, although the name can be deceiving because these still require temperatures below 135 K (-135 °C or -210 °F) to operate, which still makes them impractical for use in electronics.
Now the USC team led by professor Vitaly Kresin has discovered hints of yet another family of superconductors which work at relatively high temperatures. Specifically, they found out that while single atoms of aluminum only turn superconductive at very low temperatures (around 1 K), so-called "superatoms" (clusters of evenly spaced atoms that behave as a single atom) of aluminum turn superconductive at much higher temperatures, around 100 K.
Superconductivity takes place when so-called Cooper pairs form within a material. These are pairs of electrons that are very faintly attracted to each other and activate a mechanism whereby the electrons don’t veer off course, and therefore lose heat, whenever they bump into an imperfection within the material. Because the attractive force between the electrons, which happens only under certain conditions, is so weak (two electrons would normally repel each other), even a small amount of external energy (which could be given off in the form of heat) can upset this equilibrium. This is why superconductors only work at very low temperatures.
Kresin and team built a series of aluminum superatoms between 32 and 95 atoms large. For superatoms containing 37, 44, 66 and 68 aluminum atoms, the scientists found evidence that Cooper pairings were taking place, turning the material into a superconductor.
The researchers suggest that creating superatoms of different metals could lead to the discovery of similar superconductors that work at relatively high temperatures. While the threshold temperature was 100 K (-280 °F, -173 °C) for an aluminum superatom, different materials are likely to turn superconductive at different (hopefully much higher) temperatures.
"One-hundred Kelvin might not be the upper-temperature barrier," says Kresin. "It might just be the beginning."
Should one of these materials operate as a superconductor at room temperature, it would likely have huge impact on the worlds of electronics, medical imaging, microscopy and electric motors, just to name a few.
A paper describing the advance appears on the journal Nano Letters.