Study and optimization of ion-irradiated high Tc Josephson junctions by Monte Carlo simulations

Abstract

Abstract.High Tc Josephson nanoJunctions (HTc JnJ) made by irradiation have remarkable properties for technological applications. However, the spread in their electrical characteristics increases with the ion dose. We present a simple model to explain the JnJ inhomogeneities, which accounts quantitatively for experimental data. The spread in the slit's width of the irradiation mask is the limiting factor. Monte Carlo simulations have been performed using different irradiation conditions to study their influence on the spread of the JnJ characteristics. A "universal" behavior has been evidenced, which allows us to propose new strategies to optimize JnJ reproducibility.

Annealing effect on the reproducibility of Josephson Junctions made by ion irradiation

“…Below T J a typical RSJ like behavior is observed 15 . Tc' and ΔTc', as well as Ic and ΔIc were found to follow well the evolution of T J and ΔT J , as already observed 14 . As t is increased, T J increases and the normal resistance Rn decreases (Figure 3 inset).…”

“…where Tc is the critical temperature of a blank sample, namely 90 K. Experimentally, we have shown that for a given JJ, Tc' corresponds to the defect density in the centre of the barrier (dpa 0 ) 14 . In a JJ array there is an experimental scattering in Tc' (ΔTc'), corresponding to different dpa 0 values for each JJ with a distribution width σ dpa0 .…”

“…This generates a spread in the Josephson coupling temperature (ΔT J ), which is easier to measure experimentally. Since we have shown that ΔTc' is proportional to ΔT J over a wide temperature window 14 , we can make a direct comparison between calculations and data. We then compute the evolution of the DLD during the annealing process through random walk simulations.…”

The effects of annealing a 2-dimensional array of ion-irradiated Josephson junctions

“…• C increases the critical voltage I C R N [24,25,26,27]. The increase comes about from a much larger I C for a given temperature accompanied by a slight decrease in the voltage state resistance R N .…”

Improving the IcRn product and the reproducibility of high Tc Josephson junctions made by ion irradiation

“…[5][6][7] Good quality and highly reproducible 8-10 JJ can be built using YBa 2 Cu 3 O 7+␦ ͑YBCO͒, thanks to the optimization and control of the fabrication process. As the irradiation dose is increased, T J decreases and the spread in T J and I c increases as well, 12 reducing the reproducibility of the HT c JJ. High energy ions are used to locally disorder the superconductor through the slit and form the barrier.…”