Best Available Copy
M. von LAUE
Kaiser- Wilhelm-Institut fur physikalische und Elektro-Chemie
Berlin — Dahlem '
University of Chicago, Chicago, Illinois
The State College of Washington, Pullman, Washington
ACADEMIC PRESS INC., PUBLISHERS
New York, 1952
Best Available Copy
(a) Superconductivity was discovered in 1911 by Kamerlingh-Onnes. 1
He was the first to liquefy helium and so to produce temperatures below
10° K. With this new technique he was able to observe the continued
decrease of the electrical resistance of metals with decreasing temperature.
With mercury, in contrast to other metals, he was astonished to find that
the resistance completely vanished, almost discontinuously, at about 4.2° K
(Fig. 1-1); Today superconductivity is
.. known in 18 other metals (see Table
1— 1) whereas in others, e. g.; gold and
bismuth, the conductivity remains nor-
mal far below even 1° K. Many alloys
and compounds ' can also become super-
conducting, in particular the frequently
/ \used niobium nitride which has a tran-
sition temperature as high as 20° K.
However, among these latter substances
^ hysteresis phenomena mentioned in the
% "Introduction*' are so much more strongly
v evident that in testing the present theory
we prefer to employ only the "good"
. superconductors, i. e., the pure elements.
: ? n tne ^eal case * ne resistance vanishes
^ completely and discontinuously at a tran-
sition temperature T $ . Actually the resi-
stance-temperature curve does fall more
sharply the more the specimen is like a
single crystal and the smaller the mea-
suring current used. < Because the drop
. always occurs in a measurable tempera -
^ture* range, the experimental definition
v:- of the transition temperature is to some
^extent arbitrary. The temperature at
; / r which the direct-current resistance reaches one half of the value; it had
* just before the drop is generally given as the transition temperature, because
this can be measured accurately. However, a high-frequency investigation
to be described in Chap. 16 (f) indicates that the foot of the curve where
R 9 -i
Fig. 1 — 1. Appearance of supercon-
ductivity in mercury according to
H. Kamerlingh-Onnes (1911). The
ordinate is the resistance R;
the resistance of solid mercury
extrapolated to 0° C, is 60 ohms.
*H. Kamerlingh-Onncs. Commun. Leiden, 120b, J22h, 124c, (1911).