The influence of implanted ions on the superconducting transition temperature of transition metals and transition metal carbides

The implantation of several different ions into transition metals and transition metal carbides leads to a strong variation of T
c
. In molybdenum layers, T
c
was found to increase after implantation of B, C, N, P, As and S ions up to a maximum value of 9.4 K at concentrations of about 25 at. %. No T
c
increase has been observed for Ne, Xe and Al implants. Structure determination, resistivity measurements and additional channeling measurements on implanted Mo single crystals indicate that the T
c
-enhancement is due to a strongly distorted host lattice. Systematic studies have also been performed for other transition metals. Single crystals of NbC
0.89
and VC
0.88
have been implanted with carbon ions at different temperatures. For NbC T
c
increased from 3 to 7 K after implantation at RT and reached a maximum of 11.5 K after annealing at 1100°C. VC was found to become superconducting at about 3.2 K after implantation of carbon ions into the single crystal at 700° C. Backscattering measurements showed an improvement in the stoichiometry of the implanted regions; channeling spectra revealed that radiation damage was not completely annealed in the hot VC implants.