Heat pulse formation of superconducting phases

Current pulses of several amperes applied for ∼1 sec at T≲20 K to quasiamorphous nonsuperconducting (at 4.2 K) films of V3Si, V3Al, Nb3Sn, Nb3Ga, Nb3Al, and Nb3Si cause structural transformations to superconducting phases. The method attempts to utilize kinetics as a new variable in producing metastable superconducting phases. The suggestion is supported by the results for V3Al where Tc onsets ∼12 K or higher are achieved more readily than by other ’’equilibrium’’ growth methods. For Nb3Si several films with Tc onsets ∼12 K show the method can produce Tc’s which are higher than those obtained by hot-substrate deposition. Though much less tested, films irradiated by laser pulses at 300 K showed qualitatively similar behavior.