Low-noise YBa2Cu3O7 -PrBa2Cu3O7 multiturn flux transformers

Abstract

Epitaxial thin-film YBa2Cu3O7 flux transformers with multiturn input coils have been constructed on 1 cm2 MgO substrates using PrBa2Cu3O7 as an insulator. By coupling these to high-temperature superconducting quantum interference devices (SQUIDs) using a flip-chip technology, several low-noise magnetometers and a gradiometer have been constructed. The yield of fully working flux transformers on 1 cm2 substrates exceeds 80%, and field sensitivities at 77 K of (520±30)fT/√Hz at 1 Hz and (165±8)fT/√Hz above 10 Hz have been achieved. No evidence for excess low-frequency noise above that of the uncoupled SQUID has been found in the flip-chip magnetometers.