Thin film Bi2Sr2CaCu2O8+x Josephson junctions and direct current superconducting quantum interference devices on (001) SrTiO3 bicrystals

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Abstract
Single‐layer Josephson junctions and dc superconducting quantum interference devices(SQUIDs) have been prepared from epitaxial, laser‐deposited thin films of Bi2Sr2CaCu2O8+x on (001) SrTiO3 bicrystals with a misorientation angle of 36.8°. The current‐voltage characteristics of the Josephson junctions are of resistively shunted junction type. The I c (B) patterns look rather periodical and symmetrical but show clear irregularities in comparison to an ideal Fraunhofer‐like pattern. However, the supercurrent can be suppressed almost completely by applying an external magnetic field. The best dc‐SQUID—with a SQUID hole of 5 μm×20 μm and an estimated inductance of about 36 pH—works up to 77 K. At 76 K the flux to voltage conversion ∂V/∂Φ at the appropriate flux bias is 20 μV/Φ0. The best equivalent flux noise which was measured in the flux locked loop mode at 62 K is 25 μΦ0/√Hz at 1 Hz and 4 μΦ0/√Hz in the white noise region for f≥350 Hz, corresponding to an energy resolution of 4×10−29 J/Hz at 1 Hz and 9×10−31 J/Hz in the white noise region.

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