Study the surface oxidation effect on superconducting transition in MoGe films and nanowires.

Suppression of superconductivity (SC) in nanowires remains to a large extent poorly understood. Even for the most comprehensively studied system, MoGe nanowires, existing experimental works conflict with each other. Thus, a bosonic type of SC suppression, via quantum phase slips (QPS), was claimed for nanowires covered with Ge layer (to protect from oxidation). On the other hand, in nanowires with no such layer, fabricated both by molecular templating technique and e-beam lithography, different behavior (no QPS) was observed. Moreover, in the later wires, the suppression of the critical temperature with the cross-sectional area was a hundred times faster than that predicted by existing theories. One of the possible explanations for these discrepancies is that they are caused by magnetic moments spontaneously formed on the surface of a wire in the process of oxidation. To check this, we carried out X-ray photoelectron spectroscopy (XPS) study and transport measurements on several series of intentionally oxidized and protected MoGe films and nanowires, made of two alloys, Mo78Ge22 and Mo50Ge50. From XPS we found that the oxidation leads to the formation of several Mo oxides. The differences between oxidized and protected samples were found in thin films (below about 3 nm) We will discuss if this effect can explain discrepancies observed in nanowires.