M.Sc Thesis

M.Sc StudentBirman Daniel
SubjectHysteretic Response of Niobium-Based Direct Current
Superconducting Quantum Interference Device with
Microbridge Junctions
DepartmentDepartment of Nanoscience and Nanotechnology
Supervisor ASSOCIATE PROF. Eyal Buks
Full Thesis textFull thesis text - English Version


In this work we have fabricated, measured, and theoretically modeled, a direct current superconducting quantum interference device (DC-SQUID). A DC-SQUID is a device made of a superconducting loop, which is interrupted by two Josephson junctions. Our device was fabricated from Niobium and had microbridge Josephson junctions having a width of about 100 nm. The fabrication of such microbridges was done using focused ion beam. We electrically measured the device with direct current and with lock-in measurements and studied the dependence of the critical current on temperature and on externally applied magnetic field. A theoretical model for the SQUID was developed with an emphasis on the current phase relation of the microbridge junctions. A numerical simulation was performed to study the influence of the microbridge length on its current phase relation. The theoretical model can account for our experimental results, in which the maximal supercurrent was found to be a multi-valued function of the bias current. In this work we have demonstrated an operational SQUID that if coupled to a mechanical beam would produce a Lorentz force about 2000 times larger than the largest force possible with typical SQUID having superconducting-insulator-superconducting junctions. We have found that deviation from sinusoidal current phase relation of the microbridge has minor influence on the SQUID’s behavior, provided that the screening factor is sufficiently high.