High Field NbN Superconductor on Carbon Fibers

Abstract

Superconducting niobium nitride with a B1 structure is a good example of the powerfulness of using vapour deposition methods compared to conventional metallurgical processes. Since the discovery of Aschermann’, the superconducting transition temperature of NbN^* remained fairly constant, whereas the critical magnetic field parameter, B_c2, for NbN ranged from 8 T for diffusion nitrided samples² up to 50 T for physical vapour deposited (PVD) films³. This difference is the result of the ability to generate microstructures far removed from metallurgically processed materials. These microstructures have the desired side effect, that brittle compounds become more flexible. For a NbN film thickness of 7 μm, flexibility to a 5 mm bending radius without T_c degradation is reported⁴. Another recent result about strain effects on the critical current of NbN revealed no degradation to at least 0.7% strain⁵. It is well known that the simple B1 structure is insensitive to disorder and, therefore, superconductivity of NbN will not suffer much from neutron irradiation⁶.