Misorientation dependence of DC SQUID of YBa2Cu3O7-X grain boundary junctions on MgO bicrystal substrates

Thermal diffusion-bonded bicrystals of MgO with the configuration of [00l] tilt boundaries were incorporated as substrates to create artificial grain boundaries of epitaxial YBa₂Cu₃O_7-X (YBCO) thin films. The transport properties of the YBCO grain boundary junctions across various misorientation angles Θ, Θ=10°, 20°, 30°, 40°, have been studied. The critical current density across the grain boundaries decreased exponentially as the misoriented angle increasing. The current-voltage characteristics of the Θ=10°, 20° grain boundary junctions typically exhibited flux-flow or flux-creep like behavior; and the Θ=30°, 40° grain boundary junctions revealed a resistive shunted junction (RSJ) like I-V characteristics. The transition from strong coupling for low angle grain boundary to weak-link behavior occurred with Θ>20°. The dc SQUIDs made of θ=30° and 40° misoriented grain boundary showed periodic modulation of voltage-flux characteristics up to 77 K, IcRn = 0.4 mV, with ΔV=6 μV.