Step-edge assisted large scale FeSe monolayer growth on epitaxial Bi₂Se₃ thin films

Enhanced superconductivity of FeSe in the 2D limit on oxide surfaces as well as the prediction of topological superconductivity at the interface to topological insulators makes the fabrication of Fe-chalcogenide monolayers a topic of current interest. So far superconductive properties of the latter are mostly studied by scanning tunneling spectroscopy, which can detect gaps in the local density of states as an indicator for Cooper pairing. Direct macroscopic transport properties, which can prove or falsify a true superconducting phase, are yet widely unexplored due to the difficulty to grow monolayer films with homogeneous material properties on a larger scale. Here we report on a promising route to fabricate micron-scale continuous carpets of monolayer thick FeSe on Bi₂Se₃ topological insulators. In contrast to previous procedures based on ultraflat bulk Bi₂Se₃ surfaces, we use molecular beam epitaxy grown Bi₂Se₃ films with high step-edge densities (terrace widths 10–100 nm). We observe that step edges promote the almost strainless growth of coalescing FeSe domains without compromising the underlying Bi₂Se₃ crystal structure. (paper)