Abstract
The temperature and magnetic field dependences of the surface impedance of Nb50 wt/oTi were investigated with a TE 011-mode cavity operated at a frequency of 9.67 GHz. The results with the cavity cooled down in the earth's magnetic field show good agreement with the BCS-behaviour of the surface resistance in the Meissner state when a reduced gap, Δ(O) k BT c of 1.97, and a mean free path of 0.5 nm are assumed. Measurements in external magnetic fields up to 3 T were used to obtain the flux flow resistivity (FFR) of NbTi. The FFR obtained in this way shows a marked deviation from the phenomenological straight line behaviour ρ 1 ρ n = B H ∗ c 2 , which has been found all low- and medium-K superconductors. This indicates that the high K of NbTi leads to reduced flux flow losses at lower magnetic fields in qualitative agreement with calculations by Hu and Thompson for gapless high-K superconductors. Investigations of the temperature dependence of the ffr resulted in a resistance minimum being deeper and occurring at higher temperatures than those which have been reported for all other materials investigated to date.
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