Electrodeposition of Superconducting Iron Selenide Thick Films as a New Possible Approach to the Coating of RF Cavities

A possible strategy to maximize the efficiency of RF cavities inside haloscopes is to coat the inside of the cavity with a low-resistivity material. Currently employed for this purpose are superconductors such as Nb-Ti, Nb3Sn and ReBCO compounds. A possible alternative is the iron-based superconductor FeSe, competitive for its intrinsic physical properties and for its possibility of being electrodeposited as thick films on metallic electrodes of potentially any geometry, including curved surfaces such as those of the cavities. This chemical technique has been successfully employed in recent years for the deposition of FeSe films, but optimization of the process is still lacking in the literature, as well as studies related specifically to the coating of RF cavities. In this work, we show how the electrodeposition of FeSe can lead to thick superconducting films (approx. 1 μm) on metallic substrates. By tuning the production process, we demonstrate it is possible to reproducibly obtain samples with T<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub>(onset)∼8 K and zero resistance at temperatures above liquid He.