Current-Voltage Characteristics of Bi2Sr2CaCu2O8+δ in the C-Axis Direction

Abstract

Current-voltage (I-V) characteristics of Bi2Sr2CaCu2O8+δ single crystals were measured in the c-axis direction as a function of temperature and magnetic field parallel to the current. In order to eliminate heating effect, a voltage pulse with a width of 0.5 – 1 μs was applied for each I-V point. We found an ohmic region far below the gap voltage. The ohmic resistance increased with decreasing temperature and grew 30 times larger at 4.2 K than that at room temperature. Magnetic field strongly suppressed the critical current but did not change this ohmic resistance. These behaviors can be explained by a semiconductive shunt resistance connected in parallel to a stack of Josephson junctions. By applying two-step voltage pulses, we observed a hysteretic feature of the intrinsic Josephson junctions. Crystals with different oxygen contents showed a large variation in critical current, normal resistance, the shunt resistance at low temperature and the degree of hysteresis due to a difference in anisotropy ratios. Utilizing the bistability revealed by the hysteretic feature, the Bi2212 crystal can function as a switching device in the c-direction. A natural stack of many junctions will exhibit large response voltage, which is a great advantage for application to power devices.