YBa2Cu3O7−δ/NdBa2Cu3O7−δ/YBa2Cu3O7−δ edge junctions and SQUIDS

Abstract

YBa2Cu3O7−δ (YBCO) Josephson junctions in a ramp edge geometry with NdBa2Cu3O7−δ (NBCO) barriers were fabricated by pulsed laser deposition on (100) SrTiO3 substrates. The barrier layer thicknesses were d=100, 200, and 300 Å . The I–V characteristics of YBCO/NBCO/YBCO junctions changed from the resistively shunted junction type to flux-creeplike behavior as temperature decreased. Shapiro steps due to the ac Josephson effect clearly developed under microwave irradiation. The interface between the superconducting (YBCO) and the normal layer (NBCO) turned out to be fairly clean with small interface resistance. The mean value of the measured IcRn product for junctions with 100-Å-thick barriers was 71±34 μV at 77 K. The normal coherence length of the NBCO barrier material was ∼40 Å. The SQUIDs, made of superconductor–normal metal–superconductor junctions, showed voltage modulation at 77 K.