ScienceWeek

EARLY HISTORY OF HIGH-TEMPERATURE SUPERCONDUCTORS

The following points are made by D. Larbalestier et al (Nature 2001 414:368):

1) The potential applications of superconductors -- the name Kamerlingh Onnes (1853-1926) gave to materials that lose electric resistance on cooling below a specific transition temperature --were apparent to Onnes almost immediately. In 1913, just two years after his discovery, Onnes talked in Chicago about the design of very powerful magnets far exceeding the fields achievable by iron; these would cost as much as a battleship if made from copper and cooled with liquid air, but be affordable if made from superconducting wires. By that time he had already tested a nickel alloy coated with lead-rich superconducting solder, but this lost superconductivity at fields of less than 50 millitesla. He ascribed this unexpected setback to bad places in the wire, a problem he anticipated would soon be fixed without difficultly.

2) In fact, applications had to wait 50 more years, particularly because the physics of superconductivity in magnetic fields was seriously misunderstood. This need not have been so, because London and Shubnikov made important breakthroughs in understanding the magnetic properties of superconductors in the 1930s. By careful alloying experiments, Shubnikov pointed out the vital distinction between type I superconductors, in which currents flow only at the surface and superconductivity is destroyed by weak fields, as in Onnes's 1913 experiment, and a new type of superconductor, now called a type II superconductor, capable of carrying bulk supercurrent at high fields. The key understanding that the behavior of type II superconductors is due to quantized magnetic vortices was achieved by Abrikosov in the 1950s.