New technique holds promise for superconducting transistors

Brookhaven physicist Ivan Bozovic (pictured) says the technical breakthrough is already leading to advances in understanding high temperature superconductivity and could also accelerate the development of resistance free electronic devices. "Understanding exactly what happens when a normally insulating copper oxide material transitions from the insulating to the superconducting state is one of the great mysteries of modern physics," he said. According to the researcher. the group employed a technique called molecular beam epitaxy (MBE) to create perfect superconducting thin films one atomic layer at a time. Recently, they've shown that in such MBE created films, even a single cuprate layer can exhibit undiminished high temperature superconductivity. They've since applied the same technique to build ultra thin superconducting field effect devices that they hope allow them to achieve the charge separation, and thus electric field strength, for these critical studies. Because no known insulator could withstand the high fields required to induce superconductivity in the cuprates, the standard field effect transistor (FET) scheme didn't work for high temperature superconductor FETs. Instead, the scientists used electrolytes, liquids that conduct electricity, to separate the charges. In this setup, when an external voltage was applied, the electrolyte's positively charged ions travelled to the negative electrode and the negatively charged ions travelled to the positive electrode. However, when the ions reached the electrodes, they abruptly stopped. According to Bozovic, the electrodes' 'walls' carried an equal amount of opposite charge and the electric field between the two oppositely charged layers could exceed the 10billion volts per meter goal. This resulted in a field effect device in which the critical temperature of a prototype high temperature superconductor compound could be tuned by as much as 30 degrees Kelvin - approximately 80% of its maximal value and almost ten times more than the previous record. The scientists are now using this enhanced device to study some of the basic physics of high temperature superconductivity. "This is just the beginning," concluded Bozovic. "We still have so much to learn about high temperature superconductors. But as we continue to explore these mysteries, we are also striving to make ultrafast and power saving superconducting electronics a reality."