The density of states in four superconductors, lead, tin, indium, and aluminum, has been studied using the tunneling technique. The experimental results agree remarkably well with the Bardeen-Cooper-Schrieffer theory; however, two exceptions were found. The energy gap is not as sharp in the experiment as in the theory, but this may merely be due to imperfect samples. The density of states in lead has definite but small divergences from the theory.

• Received 16 November 1961

DOI:https://doi.org/10.1103/PhysRev.126.941