Comparison of Josephson Microwave Self-Radiation and Linewidth Properties in Various YBa_2Cu_3O_y Grain Boundary Junctions

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We have investigated the Josephson microwave self-radiation and the linewidth from different types of YBa_2Cu_3O_y(YBCO) grain boundary junctions : natural grain boundary junctions, step-edge junctions and bicrystal junctions. The Josephson self-radiation was directly observed using a total power radiometer receiver with receiving frequencies f_ltRECgt=1.7-72 GHz. All junctions exhibited microwave self-radiation peaks with intensity of order of 10^lt-12gt-10^lt-14gt W. For step-edge and bicrystal junction, they appeared at a voltage related to the Josephson frequency-voltage relation, V=n(h/2e)f , while for natural grain boundary junctions, the above relation did not hold, suggesting a Josephson medium property. For all types of junctions the observed Josephson linewidth deviated from the theoretical RSJ values due to the extra noise source in the grain boundary junction. The Josephson linewidth decreased with increasing the receiving frequency for all type of junctions. The reduction of Josephson linewidth at higher frequencies indicates that the critical current fluctuations due to a critical current spread at small bias voltages and a crystalline disorientation at the junction boundary generate an additional noise in grain boundary junctions.
社団法人電子情報通信学会の論文
1995-05-25