DC superconducting quantum interference devices fabricated using bicrystal grain boundary junctions in Co-doped BaFe₂As₂epitaxial films

Abstract

DC superconducting quantum interference devices (dc-SQUIDs) were fabricated in Co-doped BaFe2As2 epitaxial films on (La, Sr)(Al, Ta)O3 bicrystal substrates with 30deg misorientation angles. The 18 x 8 micro-meter^2 SQUID loop with an estimated inductance of 13 pH contained two 3 micro-meter wide grain boundary junctions. The voltage-flux characteristics clearly exhibited periodic modulations with deltaV = 1.4 micro-volt at 14 K, while the intrinsic flux noise of dc-SQUIDs was 7.8 x 10^-5 fai0/Hz^1/2 above 20 Hz. The rather high flux noise is mainly attributed to the small voltage modulation depth which results from the superconductor-normal metal-superconductor junction nature of the bicrystal grain boundary.