Enhancement of the critical current of intrinsic Josephson junctions by carrier injection

We present a study of the doping effect by carrier injection of high-T-c superconducting Bi-based whiskers. The current was injected in the c-axis direction, i.e., perpendicular to the superconducting planes. Superconducting properties were investigated systematically as a function of the doping level. The doping level of one and the same sample was changed by current injection in very small steps from an underdoped state up to a slightly overdoped state. We have observed that T-c versus log (j(c)) exhibits a dome-shaped characteristic, which can be fitted by a parabola. As T-c versus carrier concentration has a parabolic form, too, it can be concluded that the critical current density j(c) increases exponentially with the doping level. The electron-trapping mechanism is interpreted in the framework of Phillips' microscopic theory. In addition, the Joule heating effect in the intrinsic Josephson junction (IJJ) was controlled by carrier injection, and the effect of the non-equilibrium quasiparticle on the I-V curves of the IJJs was also discussed.