BCS theory
In 1956, Tinkham and a fellow postdoc Rolfe Glover found the direct evidence of an energy gap in the continuous distribution of energy levels in the form of a sharp rise in the optical absorption spectrum of a superconductor. The absorption spectrum observed was a direct consequence of the coherence factors of the BCS theory of John Bardeen, and along with other observations, provided the first substantive experimental confirmation of the BCS theory.