Impact of annealing and hydrogenation on the superconducting transition temperature of (TiNbMoTaW)Nx high entropy alloy nitride films

Very recently it was shown that incorporation of nitrogen into Ti _0.2Nb _0.2Mo _0.2Ta _0.2W _0.2 high-entropy alloy films leads to a considerable superconducting transition temperature T _C enhancement in corresponding (TiNbMoTaW) _1.0N _x nitrides. Here we report, independently, about the impact of subsequent annealing and the influence of additional hydrogen incorporation on these films, which should lead to a further enhancement of T _C. However, the expected T _C increase was not observed, on the contrary, both annealing of films at 800 °C in vacuum and incorporation of hydrogen into these films led to a reduction of T _C. Analysis of the results shows that in case of annealing this is related to nitrogen release from the films, in case of hydrogenation to reductions of the density of states at the Fermi level and of the electron-phonon interaction.