Magnetic field dependence of the critical current in YBa_2Cu_3O_{7-\delta}/Au/Nb ramp-zigzag Josephson junctions

TL;DR

This study investigates how small misalignments in magnetic field application affect the uniformity of flux distribution and critical current behavior in multifacet YBa2Cu3O7−δ-Au-Nb zigzag Josephson junctions, revealing sensitive dependence on alignment angles.

Contribution

It provides detailed analysis of flux inhomogeneity caused by tiny misalignments in magnetic field orientation in ramp-zigzag Josephson junctions, highlighting the importance of precise alignment.

Findings

Homogeneous flux distribution occurs only within 1-2° alignment accuracy.

Small misalignments (~0.1°) cause significant flux inhomogeneity.

Identification of a dead angle where the flux density effectively vanishes.

Abstract

We study the critical current I_c dependence on applied magnetic field H for multifacet YBa_2Cu_3O_{7-\delta}-Au-Nb ramp-type zigzag Josephson junctions. For many experiments one would like to apply a homogeneous field in the junction plane. However, even tiny misalignments can cause drastic deviations from homogeneity. We show this explicitly by measuring and analyzing I_c vs. H for an 8 facet junction, forming an array of 4\times(0-\pi)-segments. The ramp angle is \theta_r=8^\circ. The facet width is 10\,\mum. H is applied under different angles \theta relative to the substrate plane and different angles \phi relative to the in-plane orientation of the zigzags. We find that a homogeneous flux distribution is only achieved for an angle \theta_h\approx 1^\circ - 2^\circ and that even a small misalignment \sim 0.1^\circ relative to \theta_h can cause a substantial inhomogeneity of the flux density inside the junction, drastically altering its I_c vs. H interference pattern. We also show, that there is a dead angle \theta^*_d relative to \theta_h of similar magnitude, where the average flux density completely vanishes.