High‐Field Superconductivity

One does not often read original research communications that are 50 or 75 years old. Preparing an article to commemorate the 75th anniversary of the discovery of superconductivity seemed to be an appropriate occasion for reading some of Heike Kamerlingh Onnes’s original articles. Two years after his discovery, Onnes made a report to the third International Conference of Refrigeration in 1913. He reviewed the recent research of his Leiden group. This article is quite astonishing, and only extensive quotations can convey the breadth of Onnes’s conception of the possibilities of the superconducting state. Onnes commences his description of the superconducting state by describing his initial 1911 experiments on mercury, but he proceeds rapidly to sketch whole segments of the technology of superconducting magnets:

Mercury has passed into a new state, which on account of its extraordinary electrical properties may be called the superconductive state…. The behavior of metals in this state gives rise to new fundamental questions as to the mechanism of electrical conductivity.

It is therefore of great importance that tin and lead were found to become superconductive also. Tin has its step-down point at 3.8 K, a somewhat lower temperature than the vanishing point of mercury. The vanishing point of lead may be put at 6 K. Tin and lead being easily workable metals, we can now contemplate all kinds of electrical experiments with apparatus without resistance….