This is such a good paper to read. Joerg Schmalian has dug up and illustrated all the failed theories in trying to describe the phenomenon of superconductivity before the BCS theory came along. In the process, we realize how amazing BCS theory is for what it accomplished.
Abstract: Almost half a century passed between the discovery of superconductivity by Kammerlingh Onnes and the theoretical explanation of the phenomenon by Bardeen, Cooper and Schrieffer. During the intervening years the brightest minds in theoretical physics tried and failed to develop a microscopic understanding of the effect. A summary of some of those unsuccessful attempts to understand superconductivity not only demonstrates the extraordinary achievement made by formulating the BCS theory, but also illustrates that mistakes are a natural and healthy part of the scientific discourse, and that inapplicable, even incorrect theories can turn out to be interesting and inspiring.
You get a clearer picture of his intention in the introduction.
When discussing failed attempts to understand superconductivity, we must keep in mind that they are a natural and healthy part of the scientific discourse. They are an important part of the process of finding the right answers. These notes are not written to taunt those who tried and did not succeed. On the contrary, it is the greatness that comes with names like Joseph John Thompson, Albert Einstein, Niels Bohr, Léon Brillouin, Ralph Kronig, Felix Bloch, Lev Landau, Werner Heisenberg, Max Born, and Richard Feynman that demonstrates the dimension of the endeavor undertaken by John Bardeen, Leon N Cooper and J. Robert Schrieffer. Formulating the theory of superconductivity was one of the hardest problems in physics of the 20th century.
A highly recommended reading.