The critical current of miniature thin film Josephson junctions with high current densities

Abstract

Nb-Nb0,-Pb tunnel junctions with areas of about 10 x 10 pm2 and high current densities are prepared by cleaning the niobium surface in a rf glow discharge. The dependence of the critical Josephson currents on magnetic field is investigated. To a first approximation the behaviour of the critical current is described by the theory of one-dimensional junctions. Critical current densities up t~ 2 x 105 A/cma are reached. Nb-NbO,-Pb-Tiinnelverbindui~genmit Fliichen von etwe 10 X 10 ym2 und mit hohen Strorndichten werden durch Reinigen der Nioboberflache in einer HF-Glimmentladung hergestellt. Die Abhingigkeit des kritischen Josephsonstromes vom Magnetfeld wird untersucht. In erster Niiherung wird das Verhalten des kritischen Stromes durch die Theorie fur eindimensionale Tunnelverbindungen beschrieben. Es werden kritische Stromdichten bis zii 2 x 105 A/cm2 erreicht. F. DETTMAXN and P. B. WEBER where y is the phase difference between the two superconductors and [8 to 101is the Josephson penetrat*ion depth, 4 and 1, are the London penetration depths, dl and d, the thicknesses of the electrode films, t is the thickness of the barrier, jo the maximum current density, Go the flux quantum, and pcco the free space permeability. The current density in bhe barrier is given by

Self-field effects in window-type Josephson tunnel junctions

“…From Eqs. (28) with σ = 1, we have L t /L b = 0.90, in quite good agreement with the value of about 0.88 obtained from Eq. (25) same within the experimental uncertainty of a few percent.…”

“…The gradual crossover of H c from short ( << 2π) to long ( > 2π) junctions has been numerically computed 29 and it was found to be well described by the empirical relationship: H c ( ) = H c coth /π in very good agreement with the experimental findings reported in Ref. 28 . Note that in the small junction limit, → 0, we recover H c = Φ 0 /µ 0 Ld m and the Fraunhofer-like magnetic diffraction pattern (MDP).…”

“…b) is the CDP of the same sample when the control current is injected into the base electrode. The asymmetry parameter is still unchanged and the pattern slopes agree with equation(29). Other results in agreement with the theory (and not reported here) were obtained for the Nb-Nb sample of figure5(a).…”

“…The threshold curves, I c (H e ), have been the subject of many analytical, numerical and experimental works [25][26][27] . It is well known that the critical magnetic field is 7,28…”

“…The control current Î is injected: (a) into the top electrode: I c,max = 1.03 mA, Îmax = −0.46 mA and Îc = ±0.56 mA, (b) into the base electrode: I c,max = 1.03 mA, Îmax = −3.4 mA and Îc = ±4.6 mA. g is the current gain given in equations (27) or(29).…”