Properties of (Hg,Re)Ba2CaCu2Oy [100]-tilt grain boundary Josephson junctions

Abstract

[100]-tilt grain boundary Josephson junctions with misorientation of the c-axis directions have been fabricated using epitaxial (Hg0.9Re0.1)Ba2CaCu2Oy [(Hg,Re)-1212] thin films grown on SrTiO3 bicrystal substrates. Two types of the [100]-tilt junctions, that is, the mountain-type junction and the valley-type junction, of which a-b planes formed a mountain shape and a valley shape along the grain boundaries, respectively, were examined for various misorientation angles (θ). Both the types of junctions showed resistively shunted junction-type current-voltage (I-V) characteristics with relatively high characteristic voltages in a wide temperature range from 4.2to110K. The valley-type junctions exhibited properties superior to those for the mountain-type junctions, such as very low excess current and much homogeneous current distribution, which is attributed to different film growth mode near the grain boundaries. They also exhibited the products of the critical current (Ic) and the normal-state resistance (Rn) as high as 3.0–4.2, 1.0–1.4, and 0.2–0.4mV at 4.2, 77, and 100K, respectively. The misorientation angle dependences of junction parameters for the [100]-tilt junctions were compared with those for conventional [001]-tilt junctions with misorientation of the a-b plane directions. The Rn and the IcRn products for the [100]-tilt junctions were substantially larger than those for the [001]-tilt junctions. Large hysteresis in the magnetic-field dependence of Ic was observed for the applied field larger than a certain threshold value, suggesting flux penetration between the CuO2 planes.