Asymmetric high temperature superconducting Josephson vortex-flow transistors with high current gain

We have fabricated Josephson vortex-flow transistors (JVFTs) based on asymmetric parallel arrays of YBa₂Cu₃O_7-δ bicrystal grain boundary junctions. The critical current I_c and the voltage V at fixed bias current I_b were measured as a function of the control current I_ctrl through a control line inductively coupled to the array. For JVFTs with an asymmetric in-line geometry a high current gain g=∂I_c/∂I_ctrll ranging between about 20 at 40 K and 14 at 70 K was achieved. This current gain is much higher than that obtained for symmetric devices and results from the self-field effect of the electrode currents. In contrast to the current gain the transresistance r _m=∂V/∂I_ctrl of the JVFTs could not be enhanced by an asymmetric device structure. The current-voltage characteristics of the asymmetric JVFTs show pronounced step-like structures caused by the self-field of the electrode currents.