Depairing-like variation of Tc in YBa2Cu3O7−δ

High Tc Josephson Nanojunctions Made by Ion Irradiation: Characteristics and Reproducibility

“…Due to lateral straggling of the incoming ions through the 20 nm wide aperture, there is a distribution of defects along the junction, and therefore a distribution of T c´. The inset of Figure 1 displays a TRIM simulation of the defect density (dpa stands for displacement per atom), and the corresponding "local" T c´, assuming an Abrikosov-Gorkov depairing model for impurity scattering in a d-wave superconductor, which has been experimental verified [5]. For a fluence of 6×10 13 at/cm 2 for instance, the minimum calculated T c´ is of the order of 35 K (as compared to the 32 K experimental value), but the coupling temperature is almost 50 K. This is due to the proximity effect : superconducting correlations coming from high T c regions propagate within the "normal" one and set the Josephson coupling [4].…”

“…This is not the transition of the irradiated part itself T c´. Based on previous studies [5] [6] and on MonteCarlo numerical simulation using the TRIM code [7], we know T c´ for the corresponding defects densities, which appears to be much lower than T J . This becomes experimentally clear when observing the I-V characteristics of the junctions.…”

High-quality planar high-Tc Josephson junctions

“…An alternative process has been proposed to create weak links on purpose. The atomic disorder induced by ion irradiation drives HTSc cuprates towards an insulating state ; for intermediate disorder, the T c is lowered and the resistivity is increased 2,3 . Authors already succeeded in making Superconductor-Normal-Superconductor (SNS) junctions by lowering locally the T c of a HTSc film 4 .…”

“…Using TRIM code 12 and suitable assumptions, we have computed a gaussian-like distribution of defects centered on the 20 nm wide slit whose standard deviation is roughly 80 nm 13 , much smaller than a crude estimate of 150 nm or so 4 , and in good agreement with experimental observations : the normal state resistance measured corresponds to the expected width of the channel within a few percents, even for the 1 µm wide ones, confirming that the straggling is much smaller than this value ; based on the actual R(T) curve of a pristine channel, we have been able to compute the one of irradiated samples with a very good accuracy (Figure 3). The increase in resistivity and the decrease in T c as a function of the created defects have been taken from the literature 3,[14][15][16] . The resistance of the whole irradiated channel has been then calculated by integrating the resistivity over the defects distribution.…”

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

“…For small enough variations, the dispersion in T J (ΔT J ) can be taken to be proportional to that of T c ' (ΔT c '), and therefore reducing ΔT c ' allows to meet our objective. Since YBCO has a d-wave superconducting order parameter, disorder decreases the critical temperature according to a depairing AbrikosovGorkov law 15 . It has been shown experimentally that the reduction of the transition temperature of the irradiated films (T c ') with increasing irradiation damage (dpa stands for displacement per atom) in YBCO films can be expressed as 15 :…”