Superconductivity in amorphous and crystalline Re-Lu films

Abstract

We report on magnetron deposition and superconducting properties of a novel superconducting material: rhenium-lutetium films on sapphire substrates. Different compositions of Re$_{x}$Lu binary are explored from $x\approx 3.8$ to close to pure Re stoichiometry. The highest critical temperature, up to $T_{c}\approx $ 6.95 K, is obtained for $x\approx 10.5$. Depending on the deposition conditions, polycrystalline or amorphous films are obtainable, both of which are interesting for practice. Crystalline structure of polycrystalline phase is identified using grazing incidence X-ray diffractometry as a non-centrosymmetric superconductor. Superconducting properties were characterized both resistively and magnetically. Demonstration of superconductivity in this material justifies the point of view that Lu plays a role of group 3 transition metal in period 6 of the Periodic table of elements. In analogy with Re$_{0.82}$Nb$_{0.18}$, Re$_{6}$Ti, Re$_{6}$Hf and Re$_{6}$Zr, one can expect that crystalline Re--Lu is also breaking the time-reversal symmetry (this still waits confirmation). Magnetoresistivity and AC/DC susceptibility measurements allowed us to determine H$_{c1}$ and H$_{c2}$ of these films, as well as estimate coherence length $\xi (0)$ and magnetic penetration depth $\lambda _{L}(0)$. We also provide information on surface morphology of these films.