Physicists at Brookhaven National Laboratory have identified a single layer responsible for one such material’s ability to become superconducting. The technique, described in the Oct. 30, 2009, issue of Science, could be used to engineer ultrathin films with “tunable” superconductivity for higher-efficiency electronic devices.
The thinner the material (and the higher its transition temperature to a superconductor), the greater its potential for applications where the superconductivity can be controlled by an external electric field. “This type of control is difficult to achieve with thicker films, because an electric field does not penetrate into metals more than a nanometer or so,” explains Brookhaven physicist and the group leader Ivan Bozovic.
To explore the limits of thinness, Bozovic’s group synthesized a series of films based on the high-temperature superconducting cuprates — materials that carry current with no energy loss when cooled below a certain transition temperature. Since zinc is known to suppress the superconductivity in these materials, the scientists systematically substituted a small amount of zinc into each of the copper-oxide layers. Any layer where the zinc’s presence had a suppressing effect would be clearly identified as essential to superconductivity in the film.
This discovery opens a path toward the fabrication of electronic devices with modulated, or tunable, superconducting properties which can be controlled by electric or magnetic fields.