Barrier-Thickness Dependence of the dc Quantum Interference Effect in Thin-Film Lead Josephson Junctions

Abstract

The barrier-layer thickness of cross-type square Pb-PbO-Pb thin-film Josephson junctions has been varied systematically and reproducibly by employing a mask-substrate changer and a low-pressureglow-discharge oxidation technique. A series of junctions has been fabricated in which the ratio of film width w to the Josephson penetration depth AJ is varied from XJ»w to AJ«W while the width of both films is kept constant at 0.3rnm. The magnetic-field dependence of the maximum zero-voltage current in these junctions has been measured as a function of the barrier-layer thickness. For non-negligible self-fields of the tunneling currents, the field dependence follows a Fresnel diffraction pattern rather than a Fraunhofer diffraction pattern. For very thin barrier layers, the maximum zero-voltage current is eventually limited by the critical current of the Pb films. Relatively thick barrier layers, on the other hand, tend to be shorted at the edges, as can be seen from the magnetic-field dependence. The stability of Pb-PbO-Pb Josephson junctions is compared with that of Nb-NbOx-Pb Josephson junctions.

Strong Proximity Josephson Coupling in Vertically Stacked NbSe2–Graphene–NbSe2 van der Waals Junctions

“…(1).Periodic modulation of I c as a function of B field at a period of 128 G corresponds to the junction geometry with an estimation of 2 ~ 50 nm. The non-monotonic suppression of the I c maximum at each lobe and finite I c at  = n 0 (n =  1,  2, …) are possibly due to the self-field effect modifying the actual current distribution across the junction depending on its geometry,[29][30][31] which is not considered in Eq. (1).…”

“…The inset of Figure b shows the I – V characteristic curves, measured at T = 4.2 K for B = 80 G (red) and −80 G (blue). The peculiar result that the retrapping current I r was larger than I c at B = −80 G was due to the self-field effect arising from the large J c of the junction. − When a large current flows between the superconducting electrodes of the junction, the dimensions of which ( L , W ) are comparable to the Josephson penetration depth λ J , the large junction current induces a significant in-plane magnetic field. This results in a skewness of maximum peaks of I c and I r from those at zero self-field (see Figure c).…”

“…Periodic modulation of I c as a function of B field at a period of 128 G corresponds to the junction geometry with an estimation of 2 λ ∼ 50 nm. The nonmonotonic suppression of the I c maximum at each lobe and finite I c at Φ = n Φ 0 ( n = ± 1, ± 2, ...) are possibly due to the self-field effect modifying the actual current distribution across the junction depending on its geometry, − which is not considered in eq . The abrupt jumps of I c at a few finite values of B field are attributed to a sudden penetration of Abrikosov magnetic vortices into the type-II superconductor NbSe 2 , owing to slight misalignment of the applied field from the planar direction.…”

The effect of an external magnetic field on the maximum current of SNINS junctions near the critical temperature

“…A first experimental observation of the magnetic field dependence of the maximum Josephson current was obtained in work [10]. Lately, many experimental and theoretical investigations of this effect have been made for junctions of different types, which are classified as so-called "short" [11][12][13][14], with dimensions that are small compared to the Josephson penetration depth l λ J and "long" [15][16][17][18], for which l λ J . Nowadays, the investigations of the behaviour of Josephson junctions in an external magnetic field for the case of annular tunnel junctions [19,20] and junctions with a ferromagnetic interlayer are also actively developed [21].…”

Josephson Junctions With Centered Step and Local Variation of Critical Current Density

“…The first considerations [4] of non-uniform j c 's were caused by technological drawbacks leading to a variation of the effective barrier thickness by either fabrication [5] or illumination of light-sensitive barriers [6]. JJs with periodic spatially modulations of j c were intensively studied regarding the pinning of fluxons [7]- [9], the spectrum of electromagnetic waves [10], [11] or their magnetic field dependencies [12].…”