RF surface resistance in Nb3Sn thin films

We have prepared thin films of Nb3Sn by electron-beam co-evaporation and measured their surface resistance between 1.5 and 18K. As previously reported, broad transitions and excessive losses were found, indicating the presence of inhomogeneities in our materials. We describe a new deposition procedure, phase-locking, which results in more homogeneous materials. Samples made with this technique have sharper transitions and very good agreement with BCS predictions, once the residual losses (~ .01m Ω) are removed.