High temperature superconductors are today what some other time the philosopher’s stone used to be. Research done by Gennady Logvenov and his colleagues from the Brookehaven National Laboratory in Upton, NY sheds a new light on how scientists could engineer materials to obtain their desiderate: room temperature superconductors.
The Brookhaven scientists have created layered films of copper-oxide or “cuprate” materials, and have localized what makes the material superconduct into a single atomic plane.
Since 1986, physicists know that cuprates can get superconductive at relatively high temperatures (30K and more). The point at which the material gets its superconducting effects is called “transition temperature” (Tc).
Now, Logvenov and colleagues have performed an experiment that could help to point theorists in the right direction. They have created a “bilayer” film with one layer of a cuprate metal and another of a cuprate insulator, using a technique called molecular beam epitaxy. Superconductivity in such bilayers tends to manifest at the interface between the layers, so the researchers were able to isolate where the effect occurs by carefully doping atomic planes within the layers with zinc, which suppresses superconductivity.
The researchers found that when they doped the entire film with zinc, it did not superconduct at all. However, when they doped a certain plane – specifically, the second copper-oxide plane away from the interface – they found that the transition temperature for superconductivity dropped from 32 to 18 K. This, they say, is proof that that plane alone is crucial for the high-temperature superconductivity.
Theory says superconductivity can be controlled with electric fields, but these only penetrate about 1 nanometer into the film, making it difficult to realize. Knowing Lognvenov’s work, now scientists can identify the crucial plane, and it may be possible to create high-temperature superconductors to save energy and to make electronic devices much more efficient, so they could work with only a fraction of the energy necessary with classic conductors.