Soft Nanostructuring of YBCO Josephson Junctions by Phase Separation

Abstract

We have developed a new method to fabricate biepitaxial YBa2 Cu3 O7-δ (YBCO) Josephson junctions at the nanoscale, allowing junctions widths down to 100 nm and simultaneously avoiding the typical damage in grain boundary interfaces due to conventional patterning procedures. By using the competition between the superconducting YBCO and the insulating Y2 BaCuO5 phases during film growth, we formed nanometer sized grain boundary junctions in the insulating Y2 BaCuO5 matrix as confirmed by high-resolution transmission electron microscopy. Electrical transport measurements give clear indications that we are close to probing the intrinsic properties of the grain boundaries.

Noise properties of nanoscale YBa2Cu3O7−δJosephson

“…4,28 Equation (1) was used on a number of soft-patterned junctions and the extracted width was compared to the nominal width measured by AFM and SEM. 16 The values were at most differing by 40%; this shows that the width of the superconducting transport channels extracted from the magnetic pattern was very close to the measured junction widths.…”

“…Here, it is interesting to note that these values are in the same range as those found in pristine soft-nanostructured GB junctions. 16 This fact clearly reflects the strong dependence of the Josephson coupling on the stoichiometry in close proximity (length scale of coherence length) of the GB. The detrimental effect of the ion etching process during the conventional nanopatterning seems to locally kill the Josephson coupling rather than inducing a gradual decrease over the whole junction area.…”

“…A suitable superconductive nanoconnection is selected and then isolated by using FIB. By In a different study, 16 transmission electron microscopy and energy-dispersive x-ray analysis was used to confirm that the precipitate at the grain boundary is greenphase. (b) AFM scan of a 10-μm-wide grain boundary interface before the FIB procedure.…”

“…Electrical properties such as critical current density (j C ), specific resistance (ρ N ), and critical current (I C ) versus magnetic field (B) have been extensively examined 16 and have shown significant differences for the two fabrication methods. Figure 2 shows the current-voltage characteristics (IVC) for (a) a soft nanopatterned (200-nm-wide), (b) a 300-nm-wide conventionally patterned, and (c) a 200-nm-wide conventionally patterned junctions.…”

“…We have previously shown that the two methods give Josephson junctions with fundamentally different critical current density, j C , and resistivity, ρ N , values. 16 In this paper, we compare the noise data of soft nanopatterned GB junctions to various electrical transport models, which allows us to determine the nature of the biepitaxial GB barriers. Moreover, from the analysis of single charge trap states in the GB barriers, we are able to qualitatively and quantitatively assess the detrimental effect of ion milling on GBs during the conventional fabrication.…”