QUASI-PARTICLE INJECTION EFFECTS IN YBA2CU3OX-BASED PLANAR STRUCTURES AT HIGH OPERATING TEMPERATURES

The modulation of the supercurrent I-s of a YBCO bridge by the quasiparticle-injection current I-G from the YBCO/Au or YBCO/PBCO/Au junctions at temperatures of 60-85 K is determined by two effects: (1) summation of the currents I-S and I-G in the YBCO bridge, and (2) nonequilibrium suppression of I-S, by the quasiparticle injection. At a thickness of the PBCO barrier of 40 nm the modulation of I-S can be described by the current-summation effect only. For YBCO/Au structures the current gain Delta I-S/Delta I-G increases linearly with decreasing temperature, reaching the value of 2 at 60 K. Numerical simulations of the current-voltage characteristics show an increase of the effective temperature T-* of the YBCO bridge under injection only at small thicknesses of the PBCO barrier. Visualization of the voltage drop over the junction area by laser scanning microscopy shows a qualitative agreement with the electrical measurements with respect to the current summation and nonequilibrium effects.