Superconducting thin-film flux transformers of YBa2Cu3O7−x

Abstract
Using a three‐layer YBa2Cu3O7−x‐SrTiO3‐YBa2Cu3O7−x in situ laser deposition process, we have constructed thin‐film flux transformers which have pickup loops 10 mm on a side and input coils with ten turns. Each layer was patterned with a shadow mask or photolithography. The flux transformers were inductively coupled to a dc superconducting quantum interference device (SQUID) at 4.2 K to determine their transition temperature, and the temperature dependence of their critical current and coupling efficiency. The best flux transformer had a transition temperature of 77 K, and enhanced the magnetic field response of the SQUID by a factor of 9.5.