ANALYSIS BY I-V CURVES FOR INTRINSIC JOSEPHSON-JUNCTIONS OF TL2BA2CACU2OX THIN-FILMS ON MGO SUBSTRATES

We successfully observed current-voltage (IV) curves which showed the behavior of intrinsic Josephson junctions using T1(2)Ba(2)CaCu(2)O(x) (T1-2212) thin films on MgO substrates by structuring mesas and measur ing the electrical transport properties along the c-axis. For a 5x5 mu m(2) mesa, a hysteretic I-V curve was observed up to 80 K, which show ed that series-connected SIS-type junctions are formed. Compared with the critical current density (J(c)) of more than 10(6) A/cm(2) paralle l to the ab-plane, an anisotropic J(c) of 1.4x10(2) A/cm(2) along the c-axis was observed at 4.9 K. By focusing on the I-V curve at Lower bi as current, the constant voltage jumps measured at the first seven bra nches were estimated to be 26 mV. The normal resistance (R-nk) Of a un it SIS junction was estimated to be 580 Omega by substituting the meas ured voltage jump in the Ambegaokar and Baratoff relation. Using the c alculation for McCumber parameter (beta(c)), the capacitance (C-k) of the unit SIS junction was estimated to be 3.6x10(-10) F/cm(2) at 77 K. The IckRnk product was estimated to be 6.4 mV and the cut-off frequen cy (f(c)=1/2 pi RnkCk) 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 fi nally, for a 300x300 mu m(2) mesa, a resistively shunted junction (RSJ ) like curve without hysteresis was observed up to 98 K. A J(c) of 5.6 x10(1) A/cm(2) along the c-axis was observed at 6.4 K. This may be exp lained by the higher content of conductive grain boundaries for a larg er mesa area.