Improvement in the Properties of Ag-Doped YBa2Cu3O7-x Grain Boundary Josephson Junctions

Abstract

Ag‐doped YBa2Cu3O7–x (YBCO) thin films using 5 to 20 wt% Ag‐doped YBCO targets have been grown by a dc sputtering technique on SrTiO3 bicrystals. Critical currents of 4 to 5 × 106 A/cm2 at 77 K were measured in YBCO films doped with 5 wt% Ag which has been found to be higher than the value of 1 × 106 A/cm2 measured in undoped samples. The normal resistivity decreases by a doping of 5 wt% Ag and increases for higher Ag concentrations. The critical temperature, Tc, of the Ag‐YBCO films remained unchanged at 92 K as in the undoped YBCO samples. An IcRn product of 170 μV at 77 K was found in Grain Boundary Josephson junctions (GBJJs) with 5 wt% Ag, compared with the value of 100 μV measured in undoped samples at the same temperature. Current–voltage characteristics were measured in GBJJs, showing Shapiro steps under microwave radiation and Fraunhofer patterns with an external magnetic field. The improvement in the normal and superconducting properties of Ag‐doped YBCO films has been interpreted using the De Gennes model to establish that YBCO containing metallic Ag addition shows a superconductor–normalmetal–superconductor (S–N–S) behavior, thereby the Ag‐doping enhances the weak link behavior and is, therefore, appropriate for electronic applications.

Fabrication and Transport Characteristics of YBCO Step‐Edge‐Based Josephson Junction on Revived MgO Substrate

“…The primary requirement for thin film deposition is a clean substrate surface, and several oxide substrates have been used for the growth of YBa 2 Cu 3 O x (YBCO) high T c superconducting thin film, including SrTiO 3 , LaAlO 3 , sapphire, and MgO. [ 1–15 ] Among all these oxide substrates, single‐crystal MgO substrates are favored for the high T c superconducting thin films deposition due to their low index of refraction ( n = 1.73), high melting point of 2976 °C, low dielectric loss, similar thermal expansion coefficient as that of YBCO thin films, low cost, and growth of epitaxial development of YBCO thin films formed on them despite a considerable lattice mismatch (≈of 9%). [ 16–20 ] Various devices, including step‐edges, Josephson junction (JJ)‐based devices, and superconducting quantum interference devices (SQUIDs), are made with a thin film of YBCO grown on MgO substrates.…”