UI physicists have fabricated arrays of sub-micron-sized superconducting "islands" on metallic films and used them to study changes in the transition to superconductivity based on island spacing and thickness. They discovered that such systems may be an ideal medium for understanding and controlling the properties of a theoretically forbidden zero-temperature metallic state. Read their paper in Nature Physics. High-resolution image.
Written by Serena Eley and Celia Elliott
In 1958, Dr. Philip Anderson, a future Nobel Laureate, made a groundbreaking prediction. At zero temperature in 1D and 2D solids, the diffusive motion of electrons scattering off impurities ceases, and there is no long range electron transport. In other words, 1D and 2D systems no longer conduct like standard metals at zero-temperature. Although this theory has accurately described the low-temperature behavior of many materials, systems ranging from 2D semiconductors to disordered superconductors have in fact shown evidence of this forbidden zero-temperature metallic state.
Determining the origin and characteristics of such metals has attracted intense theoretical and experimental interest over the past two decades. Contributing to these efforts, the Mason research group at the University of Illinois focuses on novel model systems of 2D superconductors, systems which have been predicted to exhibit these unusual metallic states as the temperature approaches zero.
"In particular, we created arrays of physically separated superconducting islands placed on normal metal films, and measured the temperature-dependent transition to the superconducting state as a function of the island separation," said graduate student Serena Eley.
"We found two surprising results: first, the long-range communication between the islands occurs in a way that cannot be explained by current theories. Second, the progressive weakening of superconductivity with increasing island spacing suggests that arrays with even further spacing would be metallic at zero temperature."
Serena Eley, Sarang Gopalakrishnan, and Nadya Mason in their lab at the University of Illinois. Not shown is co-author Paul M. Goldbart, Georgia Tech. The work reported by the UI group in a recent paper in Nature Physics is the first study of an inhomogeneous superconducting system that systematically approaches a zero-temperature metallic state. Furthermore, the results suggest that such superconductor-normal-metal systems may be an ideal medium for tunably controlling the properties of this strange metal.