Current amplification in high-temperature superconductor current injection three-terminal devices

摘要

Current injection into superconducting microbridges has been studied for state-of-the-art YBa_(2)Cu_(3)O_(7-x)/SrTiO_(3)/Au (YBCO/STO/Au) planar heterostructures based on c-axis oriented YBCO layers. By injecting a gate current I_(g) into the YBCO channel of these three-terminal devices the critical current I_(c) could be reduced up to a gain factor G≡-dI_(c)/dI_(g)～5 at 77 K. G is found to be roughly proportional to the superconducting quality of the samples as expressed by the critical current density J_(c) of the YBCO channel. At least for our high-quality samples, this I_(c) suppression is shown to be mainly due to the perturbation of the electronic superconductive equilibrium state by quasiparticles associated with the injection of the gate current. However, this basic mechanism for the current-injection-based transistor principle was in our experiments always accompanied by substantial parasitic effects, such as current summation and Joule heating due to electric power dissipation in the ultrathin STO barrier. This reduces the efficiency of the transistor mechanism and thus the hopes for THz operation of such devices.