Correlation of YBa2Cu3O7 step-edge junction characteristics with microstructure

Abstract

Current-voltage characteristics, Josephson radiation spectra, and critical current versus magnetic-field dependences were measured in epitaxial, c-axis YBa2Cu3O7 step-edge Josephson junctions (SEJs) on SrTiO3 and LaAlO3 substrates with various step angles α. The results were correlated with microstructural data to determine the origin of the observed weak-link behavior. It was shown that on steps with α≳45° the SEJ is a series connection of two weak links unambiguously correlated with the occurrence of two 90° tilt grain boundaries. On steep steps, α≥70°, the boundary at the upper step edge has, on average, the (103) symmetry, while the lower one is predominantly of the basal-plane-faced (010)(001) type. Correspondingly, one link is weaker than the other, with the weaker link originating on the (010)(001) boundary. However, others have shown that analogous grain boundaries in planar (103) and biepitaxial a-axis/c-axis films do not exhibit a strong magnetic-field dependence of critical current, which is characteristic of a weak link. Hence, it is proposed that the weak-link behavior of boundaries on step edges originates from their defect structure.

High-transition-temperature superconducting quantum interference devices

“…9(b)]. This technique, initially realized by Simon et al (1991), was subsequently refined by several groups Sun, Gallagher, Callegari et al, 1993;Herrmann et al, 1995;Pettiette-Hall et al, 1995;Yi et al, 1996). Common substrate materials are SrTiO 3 and LaAlO 3 .…”

“…It has been proposed that the grain boundaries formed at step edges behave as junctions because of their defect structure (Herrmann et al, 1995), since 90°g rain boundaries in planar films do not exhibit such behavior. Thus the properties of step-edge junctions depend strongly on the microstructure of the milled step and on the film-growth conditions, leading to greater spreads in parameters than for bicrystal junctions.…”

Superconducting and electro-optical thin films prepared by pulsed laser deposition technique

“…The goal of our investigation was to establish an IBE-process which produces a steep clean step angle <708 as a base for step edge junctions in order to reduce the spread in the 1/f-noise of our rf-SQUIDs. Using a rotating substrate and an angle of incidence of 458 of the ion beam with regard to the surface of the substrate we achieve a clean step with a step angle <508 (process 1) [12]. An alternative method is to align the direction of a ®xed ion beam parallel to the long edge of the trench forming photoresist mask (process 2).…”

d-Wave YBCO dc superconductive quantum interference devices (dc SQUIDs)

“…This technique, initially realized by Daley et al (1990), was subsequently refined by several groups (Herrmann et al, 1991(Herrmann et al, , 1995Sun et al, 1993;Yi et al, 1996). Common substrate materials are perovskites (001) SrTiO 3 and (001) LaAlO 3 .…”