1. W.L. McMillan and J.M. Rowel1, Superconductivity, ed. by R.D. Parks (Marcel Dekker, New York, 1969). For a list of the materials studied by tunneling, see R.C. Dynes, Sol. St. Comm. 10, 615 (1972) and P.B. Allen and R.C. Dynes, Phys. Rev. B12, 905 (1975).
2. L.Y.L. Shen, Superconductivity in d- and f-Band Metals, ed, by D.H. Douglass ( AIP, New York, 1972 ).
3. L.Y.L. Shen, Phys. Rev. Lett. 24, 1104 (1970).
4. J. Bostock, V. Diadiuk, W.N. Cheung, K.H. Lo, R.M. Rose, and M.L.A. MacVicar, Phys. Rev. Lett. 36, 603 (1976) and references therein.
5. Klaus Gartner, Dissertation, Abteilung fur Elektrotechnik an der Ruhr-Universitat Bochum.