Strain Has Major Effect

Magneto-optical image of magnetic fields in superconductor

The effect, which is reversible, adds a new dimension to designing superconducting systems - particularly for electric power applications - and it also provides a new tool that will help scientists probe the fundamental mechanism behind why these materials carry current with no resistance.

The measurements revealed a 40 percent reduction in critical current, the point at which superconductivity breaks down, at just 1 percent compressive strain. This effect can be readily accommodated in the engineering design of practical applications, NIST project leader Jack Ekin says, but knowing about it ahead of time will be important to the success of many large-scale devices.

The effect was measured in three types of yttrium-barium-copper-oxide (YBCO), a brittle ceramic considered the best prospect for making low-cost, high-current, superconducting wires. The researchers developed a “four point" bend technique that enables studies of superconducting properties over a wide range of uniform strain at high current levels. The superconductor is soldered on top of a flexible metal beam, which is then bent up or down at both ends while the critical current is measured.

The discovery is the first major reversible strain effect found in practical high-temperature superconductors, which generally have been tested under smaller tensile strains only, or at strains so high they caused the material to break down permanently. The newly discovered effect is totally reversible and symmetric for both compressive and tensile strains, suggesting it is intrinsic to the fundamental mechanism of superconductivity in YBCO.; Source: National Institute of Standards and Technology (NIST)