Upper limit for superconducting transition temperature in Eliashberg-McMillan theory

Abstract

We present simple qualitative estimates for the maximal superconducting transition temperature, which may be achieved due to electron - phonon coupling in Eliashberg-McMillan theory. It is shown that in the limit of very strong coupling the upper limit for transition temperature is determined in fact by a combination of atomic constants and density of conduction electrons.

2 pages, minor typos corrected