Josephson Structures Research Articles

Transport critical current in bulk sintered YBa 2Cu 3O 7 in weak magnetic field

The magnetic field dependence of the dc critical current carried by sintered YBa 2Cu 3O 7 samples have been investigated at different temperatures close to the critical temperature T c. The critical current was measured by a linear four probe configuration on samples in a suitable shape, by detecting the occurrence of a voltage of about 1μV. A strong reduction of the critical current has been observed for field values smaller than the lower critical field Bc 1. This behavior is discussed in terms of weak coupling between different superconducting regions in the material. The low field data show an excellent agreement with the theoretical magnetic field dependence computed for Josephson structures.

Josephson effects in the Ba-Y-Cu-O compounds.

A point-contact Josephson junction between a bulk Ba-Y-Cu-O compound (${T}_{c}\ensuremath{\sim}90$ K) and a Nb needle has been made. The $I\ensuremath{-}V$ characteristics under microwave radiation show Shapiro steps, confirming the Josephson nature of the formed contact. Spin-singlet superconductivity in the Ba-Y-Cu-O system is implied from the voltage of the steps. The temperature dependence of the critical currents suggests that the Josephson junction if formed between Nb and another material with much higher ${T}_{c}$. Internal Josephson structure within the bulk ceramics is not found in the Ba-Y-Cu-O system.

Analysis on dc characteristics of Josephson structures by the one-dimensional Green’s function method

Calculations on dc behaviors of Josephson structures in pure limit are made based on the one-dimensional Green’s function method. A close resemblance is found to exist between the behavior of the double-barrier-tunneling system and that of the short microbridge.

Vanadium-based light-sensitive Josephson junctions

Vanadium-based superconducting tunnel junctions have been realized using a photoconducting film as barrier. A preliminary characterization of VCdSIn Josephson structures has been performed taking into account also their light-sensitive behaviour.

Numerical analysis of vortex motion on Josephson structures

The one-dimensional and two-dimensional sine-Gordon equations with dimensionless loss factors and unitless normalized bias are numerically calculated by computer. The results are presented for accelerations, velocities, collisions, coupled states, and two-dimensional propagation of solitons.

Josephson junction interference grating

The maximum current through multiple Josephson structures as a function of applied magnetic field is presented. Particular emphasis is placed on the Josephson penetration depth effects and geometrical considerations. The symmetrical and asymmetrical current feed two-, three-, four-, and five-junction gratings are analyzed and discussed. The Josephson penetration depth is shown to control the amplitude of the interference and diffraction patterns of the interference grating. In addition the interior-junction-length/interference-loop-area product is shown to control the operating mode of the interference grating. The dependence of the magnetic field sensitivity and interference pattern amplitude on the number of junctions is discussed.