Superconductivity in amorphous and crystalline Re-Lu films

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.