Analysis by I-V Curves for Intrinsic Josephson Junctions of Tl_2Ba_2CaCu_2O_x Thin Films on MgO Substrates (Special Issue on Basic Properties and Applications of Superconductive Electron Devices)

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We successfully observed current-voltage (I-V) curves which showed the behavior of intrinsic Josephson junctions using Tl_2Ba_2CaCu_2O_x (Tl-2212) thin films on MgO substrates by structuring mesas and measuring the electrical transport properties along the c-axis. For a 5×5 μm^2 mesa, a hysteretic I-V curve was observed up to 80 K, which showed that series-connected SIS-type junctions are formed. Compared with the critical current density (J_c) of more than 10^6 A/cm^2 parallel to the ab-plane, an anisotropic J_c of 1.4×10^2 A/cm^2 along the c-axis was observed at 4.9 K. By focusing on the I-V curve at lower bias current, the constant voltage jumps measured at the first seven branches were estimated to be 26 mV. The normal resistance (R_<nk>) of a unit SIS junction was estimated to be 580Ω by substituting the measured voltage jump in the Ambegaokar and Baratoff relation. Using the calculation for McCumber parameter (β_c), the capacitance (Ch) of the unit SIS junction was estimated to be 3.6×10^<-10> F/cm^2 at 77K. The I_<ck>R<nk> product was estimated to be 6.4 mV and the cut-off frequency (f_c=1/2πR<nk>C_k) was calculated to be 3.1 THz at 77 K. The J_c and the hysteresis decreased with an increase in the mesa area, and finally, for a 300×300 μm^2 mesa, a resistively shunted junction (RSJ) like curve without hysteresis was observed up to 98K. A J_c of 5.6×10^1 A/cm^2 along the c-axis was observed at 6.4K. This may be explained by the higher content of conductive grain boundaries for a larger mesa area.
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1997-10-25

Analysis by I-V Curves for Intrinsic Josephson Junctions of Tl_2Ba_2CaCu_2O_x Thin Films on MgO Substrates (Special Issue on Basic Properties and Applications of Superconductive Electron Devices)

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