Transport characteristics of Tl2Ba2CaCu2O8 bicrystal grain boundary junctions at 77 K

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Abstract
We report the fabrication and characterization of thin‐film grain boundaryjunctions in Tl‐based superconductors on bicrystal substrates. Post‐deposition processed Tl2Ba2CaCu2O8 films were grown on bicrystal SrTiO3 substrates, with varying degrees of misorientation angle θ. Critical current densities and current‐voltage curves had a strong dependence on θ. For θ≥10°, there was a two‐to‐three order of magnitude reduction in critical current density, and for θ≥20°, the current‐voltage curves displayed resistively shunted junction behavior. These high angle grain boundaryjunctions have features at 77 K that are attractive for device applications, including sharp voltage onsets, well‐behaved dc magnetic and rf field dependence, I cR n products as large as 300 μV, and low 1/fnoise. Simple dc superconducting quantum interference devices fabricated with these junctions exhibited transfer functions of up to 30 μV/Φ0 at 77 K.