Quantum electrodynamics of cold deposited granular aluminum

increasing interest in the superconducting quantum circuits community
because of its promising characteristics such as its tunable kinetic inductance,
low microwave losses, high in-plane critical magnetic field,
and a higher critical temperature compared with pure Al.
In general, the critical temperature of a grAl film depends on its resistivity
until it reaches a superconducting-to-insulator transition. For
samples evaporated at room temperature, a maximum of around 2.2K
is reached for resistivity of about 1000 𝜇Ω. The critical temperature
rises even above 3K when grAl is deposited on a substrate held at a
lower temperature of 100K.
This project aims to answer the question of increased Tc, which is
yet to be understood microscopically, and other consequences of cold
deposition, such as how a generally smaller – while more homogeneous
– grain size positively affects the electrodynamics of the film. The testbed
used to characterise the electrodynamics are stripline resonators
fabricated entirely from cold-deposited grAl, and measured in a cylindrical
copper waveguide sample holder at cryogenic temperatures.