Quasiparticle injection effects in YBa2Cu3Ox-based planar structures at high operating temperatures

Abstract

The modulation of the supercurrent Is of a YBCO bridge by the quasiparticle-injection current 1 o 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 Is and 16 in the YBCO bridge, and (2) nonequilibrium suppression of Is by the quasiparticle injection. At a thickness of the PBCO barrier of 40 nm the modulation of Is can be described by the current-summation effect only. For YBCO/Au structures the current gain A/s/A/6 increases linearly with decreasing temperature, reaching the value of 2 at 60 K. Numerical simulations of the currentvoltage 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.

Quasiparticle injection effect of aYBa2Cu3O7−

“…[2][3][4] Previous studies on the nonequilibrium state of high-T c superconductors by quasiparticle injection current, however, have so far not provided useful information, because of the imperfect geometries in these measurements. In previous reports, [5][6][7][8][9] most measurements were performed using samples with cross-line junction geometry. In this geometry, both the injection current and the transport current flow in a YBCO film in parallel, yielding a pairbreaking effect by the injection current itself as well as by the transport current, which made the observed characteristics quite asymmetric with respect to the direction of current flow.…”

“…The observed characteristics were nearly symmetric with respect to the relative direction of the injection current and the film critical current, in contrast to previous reports. [5][6][7][8][9] It is understood that, since J c (J inj ϭ0)ϵJ c0 ӷJ inj (J c ϭ0)ϵJ ic , the quasiparticle injection effect is significantly greater than the current pair-breaking effect for this sample, even if some current spread is taken into account. At 4.2 K the YBCO film critical current (I c ϭ62 mA) was suppressed to zero at critical injection current I inj ϭI ic ϭ30 mA, and the current gain as defined by I c /I ic was about 2.…”