Abstract

The Elishberg generalization of BCS theory includes a parameter λ describing the strength of the electron - phonon coupling constant.¹ In 1987, P. B. Allen made the suggestion that λ might be measured in the metallic superconductors using femtosecond thermomodulation (pump - probe) spectroscopy.² Such experiments³,⁴ have been performed on Cu and Au, although not in the context of measuring λ. Here we report the results of systematic femtosecond thermomodulation measurements of λ in metallic thin films of Cu, Au, Cr, Ti, W, Nb, V, Pb, NbN, and V3Ga. The agreement between our measured λ values and those obtained by other means is excellent, thus confirming Allen’s theory. This method to measure λ has several advantages over other techniques: it is the most direct measure of λ〈ω²〉, it works at room temperature, it can be applied to both superconducting and non-superconducting samples, and it is not affected by interactions competing with superconductivity such as the antiferromagnetism in Cr.

© 1990 Optical Society of America