Reproducible High-T _c SNS Josephson Junctions and DC-SQUIDs

Abstract

Reproducible high-T_c YBa₂Cu₃O₇/Ag/YBa₂Cu₃O₇ Josephson junctions have been fabricated using an entirely in-situ step-edge technique. Josephson junctions have been produced with IcRn products up to 4.6 mV at 4.2 K and normal resistances up to 5 Ω. The expected modulation of the critical current in a magnetic field is observed in single junctions as well as dc SQUIDs. The devices exhibit a well-defined supercurrent from 4.2 K to 87 K. The lowest measured flux noise sensitivity of a dc SQUID at 4.2 K is 1.4 × 10⁻⁶ Φ_O/${\phi _0}/\surd Hz$ at 2.5 kHz leading to an energy sensitivity of 2.8 × 10~31 J/Hz. At 10 Hz the best measured flux noise at 4.2 K is 2.6 × 10⁻⁵ Φ/${\phi _0}/\surd Hz$ leading to an energy sensitivity of 4.8 × 10⁻²⁹ J/Hz.