Giant proximity effect paves way for ultra fast, superconducting electronics

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Sandwiched superconductors engineered to function at higher temperatures could soon be used in new, ultra fast, superconducting electronics according to US researchers.

In collaboration with scientists from the Paul Scherrer Institute (PSI) and the University of Z├╝rich in Switzerland, Brookhaven National Laboratory physicist Ivan Bozovic discovered that sandwiching a barrier layer between two superconductors made it superconducting at significantly higher temperatures. He believes the breakthrough could lead to the realisation low power consumption, ultra fast superconducting electronic devices. "For many years, we have known about a 'proximity effect', that superconducting electron pairs from one superconducting electrode can drift and penetrate a very thin metallic layer and then reach the other superconducting electrode without losing their coherence," he said. "More recently, we have observed a mysterious 'giant proximity effect' in copper oxide materials - cuprates - when supercurrent flows through much thicker barriers." Because thicker layers are easier to fabricate and work with, Bozovic says taking advantage of the new method could make it much easier to achieve on chip device uniformity - the requirement that all devices on an electronic chip have similar parameters. "This has been a major technical hurdle for large scale, integrated superconducting electronics," he noted. To explore the new effect, the team engineered complex cuprates using a process called molecular beam epitaxy. It synthesised samples of thin films containing layers of lanthanum cuprate superconductors doped with strontium to various levels, to create a series with varying transition temperatures. The Brookhaven samples were studied at PSI using a technique called low energy muon spin rotation to detect superconductivity in each sample's outer and inner layers. By mapping the magnetic fields for each structure, the scientists observed the giant proximity effect and found that a thick barrier of superconductor with a Tc of 5 Kelvin could transmit supercurrent at a temperature four times higher, if it was sandwiched between two superconductors with a Tc of 40 Kelvin. Their results also proved that the entire barrier layer was affected by the effect. "In addition to its potential importance for superconducting electronics, the giant proximity effect could also be an important hint of what is going on in cuprates," Bozovic concluded. "Discovering that mechanism could open up a whole new field for engineering superconductors with desired properties." The findings have been published in the 12 April edition of the online journal Nature Communications.