Superconductivity in β-Tungsten Films
- 1 November 1968
- journal article
- research article
- Published by AIP Publishing in Journal of Applied Physics
- Vol. 39 (12), 5548-5556
- https://doi.org/10.1063/1.1656012
Abstract
Evaporated tungsten films were found to have a superconducting transition temperature Tc of 3.2°K as compared to the bulk value of 0.01°K. Structural study of the electron‐beam‐evaporated W films was carried out by both x‐ray and electron diffraction techniques. It was found that films prepared at pressures >10−7 Torr and evaporation rates Tc of these films is due to the presence of the β phase. Films prepared at 3×10−9 Torr are pure α‐W and they did not superconduct down to 1°K. The superconducting energy gap Δ(T) of the β‐W films prepared at 5×10−5 Torr and 25 Å/min was determined by tunneling in W‐B‐M junctions, where B is the plasma‐grown oxide barrier on W and M stands for Sn, Pb, and Au counterelectrodes. The temperature dependence of the energy gap Δ(T)/Δ(0) vs T/Tc followed the BCS curve remarkably well. The ratio 2Δ(0)/KTc varied between 2.32 to 3.64 as against the BCS value of 3.53, corresponding to the variation in Tc between 3.1° to 3.3°K, respectively. The relative amounts of the α and β phases present were estimated from the tunneling experiments. The variations in Tc, 2Δ(0), and 2Δ(0)/KTc are related to the relative amounts of α and β phases present in the composite film and their connectivity.Keywords
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