Far-infrared laser spectroscopy ofV3Si

Abstract

We have measured the ratio of the superconducting to the normal-state transmissions, $\frac{T_s}{T_n}$, in two thin films of ${\mathrm{V}}_3$Si with a new optically pumped far-infrared laser spectrometer. The laser system gave exceptional signal-to-noise ratios with room-temperature detectors. The data could not be well fitted with the usual Mattis-Bardeen result but could be explained by the Leplae formulation which includes the effects of a finite scattering time. Our analysis gave a value $\frac{2\Delta }{k{T}_c}=3.76\mathrm{}\pm 0.1$ for the better of the two films ($T_c=15.7\mathrm{}$ K) in good agreement with tunneling determinations and with fewer possibilities for surface problems. We observed features below the gap energy in both samples whose origin is not understood.