Ultrafast Machining of High Temperature Superconductor Nanostructures for Novel Mesoscale Physics

The high temperature superconductor YBa2Cu3O7-x (YBCO), with its critical temperature above the boiling point of liquid nitrogen, promised to make the use of superconductors in industrial applications affordable. When focussing on electrical applications such as antennas and sensors, patterning of the superconducting thin films is a necessity. Among the different patterning techniques, including lithography, mechanical scribing, and focussed ion beam, laser machining of YBCO has been continuously studied since 1988 due to its design flexibility and the absence of chemicals. One thing that is still not adequately understood is the nature of laser induced damage on YBCO, and to what proportion it affects the superconducting properties of YBCO, and its relation to feature size. In this work, the physical and electrical damage induced by an ultrashort pulse laser was investigated by scanning electron microscope (SEM) characterization and transport measurements over a range of stepwise machined YBCO microbridges. Assuming the damage is limited to the machined edge, an electrical machining limit of 550 nm was determined for a femtosecond laser (1030 nm, 350 fs). Additionally, Raman spectroscopy was used to identify spectral changes caused by degradation. While transport and Raman measurements are commonly used separately to evaluate YBCO, our approach links both techniques as a new method for quick measurements during the laser processing to identify thermal damage. The Ba/Cu2 Raman ratio was compared to the change in critical current density of thin films and bridges. After evaluating the machining limitations, the femtosecond laser was also used to create centimetre-scalesuperconducting microwave emitters. To finalise this work, a setup to laser machine YBCO, while in its superconducting state, has been developed.