Numerical optimization of nano-sized SQUID-on-tip characteristics

SQUID-on-tip (SOT) is the most sensitive magnetometry device to date, designed as a superconducting loop at the apex of a scanning tip with nearly vertical biasing leads. Here we examine the static and dynamic properties of such a SOT as a function of the 3D geometric features of the device as close as in reality, using state-of-the-art (Ginzburg–Landau) GL simulations. We find that the gradient of the phase of the order parameter in the perimeter of the loop, which relates to the screening current in response to the magnetic field, is primarily enhanced in a SOT with narrow loop arms. This decreases the critical current of the device but makes the critical current less sensitive to the penetrating field, which is beneficial for the device’s sensitivity at a constant biasing current in a broader field range. We further show how constriction in the arms of the loop can further enhance the sensitivity. Taken together, our results offer engineering solutions for the tailored performance of SOT devices in desired conditions.