A surprising new superconductor

　　Last September, CIRES chemist and instrument designer Don David and colleagues Dave Pappas and Xian Wu at the National Institute of Standards and Technology (NIST), discovered a powerful new plated metal combination that superconducts at easily attained temperature, paving the road in the development of supercomputers.

　　Now, the team has published a new “recipe” – an ultrathin layer of rhenium (Re) sandwiched between layers of gold, each measuring 1/1000th the diameter of a human hair that can superconduct at critical temperature over 6Kelvin.

　　"The sheer magnitude of the critical temperature was unexpected," said David. "We had been thinking for a while about ways to impart superconducting properties to gold and copper films, and we were surprised at how robust and effective the thin layer of electroplated Re was."

　　The team said that the electroplated Re is ideal for use in circuit boards to achieve ultrafast, next-generation computing applications because it superconducts at higher, easier-to-achieve critical temperatures, is easy to work with mechanically, non-toxic, and melts at high temperatures.

　　The team has been looking at electroplating – the process of passing an electrical current through an aqueous solution of a dissolved metal to create a metal coating on a submerged object – plating instruments like charged-particle optics and components for cryogenics applications, and in this case, circuit boards for a team at NIST.

　　Presently, CIRES is looking for a metal plating that might be superconducting for the Pappas's Quantum Processing Group at NIST. The team found success with Re: a hard, trace metal, with a high melting point.

　　Testing for electrical resistance, the team found it superconducted up to 6K, well above the boiling temperature of liquid helium (4.2K). The team is now investigating the role of hydrogen incorporation, interfaces, and strain on the enhanced superconducting temperature. But whatever the reason for the enhancement, being able to electroplate a superconductor is a giant step forward in the creation of tomorrow's high-performance, superconducting computers.

　　Superconductors aren't new, but the new paper presents evidence that electroplated Re may be the best material found to date for superconductive computer circuit board construction.

　　Many other superconductive materials, like mercury or lead, are difficult to work with mechanically, have poor soldering properties, or melt at too-low temperatures. The electroplating process would be easily scaled-up to mass-production, adds David.