Fabrication and characterization of cryogenically grown granular aluminum films

Abstract

The thesis investigates the fabrication and superconducting properties of cryogenically grown granular aluminum thin films, with a focus on understanding how deposition parameters influence superconductivity. Using thermal evaporation techniques across a wide substrate temperature range, including an unprecedented 25 K regime, the study systematically correlates growth conditions (such as evaporation rate and oxygen flow) with film morphology and superconducting behavior. A dome-like dependence of the superconducting transition temperature (Tc) on resistivity is observed and refined, with 25 K films exhibiting the highest Tc and sharpest dome. Additionally, contrary to conventional assumptions, a clear dependence of Tc on film thickness is found, revealing enhanced superconductivity in thinner films. The work provides a detailed phase diagram, explores paraconductivity, and examines Kondo-like effects, establishing granular aluminum as both a platform for studying disorder-driven superconductivity and a promising material for quantum technologies.