Superconductivity was discovered one hundred years ago. The history of its explanation is tied closely to the development of quantum physics in the 20th century. Early theories of superconductivity attempted to treat the phenomenon as a limiting case of normal metallic conductivity and related it to the chemical structure of the superconducting materials. The discovery of the Meissner-Ochsenfeld effect in 1933 led to the first thermodynamical theories, which established superconductivity as a new phase of matter. In 1935, Fritz and Heinz London developed the concept of a macroscopic quantum state. Their idea was crucial for both the 1950 phenomenological theory of

Superconductivity after BCS
—
"on
-
line computing" between experiment and
theory

Johannes Knolle, Christian Joas


Superconductivity was discovered one hundred years ago. The history of its explanation
is tied closely to the development of quantum physics in the 20th century. Early theories
of superconductivity attempted to treat the phenomenon as a limiting case of no
rmal
metallic conductivity and related it to the chemical structure of the superconducting
materials. The discovery of the Meissner
-
Ochsenfeld effect in 1933 led to the first
thermodynamical theories, which established superconductivity as a new phase of
m
atter. In 1935, Fritz and Heinz London developed the concept of a macroscopic
quantum state. Their idea was crucial for both the 1950 phenomenological theory of
superconductivity by Ginzburg and Landau and for the 1957 microscopic Bardeen
-
Cooper
-
Schrieffer

theory of superconductivity, which constitute the basis of
the

modern
understanding of superconductivity.

While experimentalists in the field quickly accepted the
„BCS“
theory of
superconductivity,
many

notable theorists remained skeptical for almost a de
cade. The
objection that the theory violated general gauge invariance was
resolved

rather quickly
by, among others, Anderson, Bogoliubov, and Nambu, who rederived the theory from
microscopic considerations within the framework of the recently
-
developed qua
ntum
field theory of many
-
bod
y systems. A second objection
—
that the BCS theory was unable
to account for su
perconductivity quantitatively
—
p
ersisted much longer: While
it

was
able to describe superconductors qualitatively, it failed at predicting properties

of
specific superconductors, such as their critical temperature, or to explain which
materials would be superconducting and which would not.

Only the tunneling experiments conducted by Giaever in the early 1960s led to a rush
towards a quantitative theory

of superconductivity, which was based on Eliahsberg's
strong
-
coupling theory. For the solution of the complicated systems of coupled integral
equations arising within this approach, physicists began to use computers that had
originally been developed for
military applications.
In our talk, w
e study the role of
computers
and numerical computations
in the development of a
truly
quantitative
theory of superconductivity. Interactive numerics, so
-
called "on
-
line computing," and a
new generation of scientists
,

w
ho were trained both in using computers and in quantum
field theory, change
d

the relation between experi
ment and theory in the field

and had a
lasting influence on the practice
s

of modern quantum physics and materials science
.