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Various types of thin-film dc gradiometer SQUIDs with integrated pickup loops were investigated. The SQUIDs were prepared on a 5 mm × 10 mm chip in the well developed Nb-NbO x -Pb/Au/In technology. It was shown that the SQUIDs work in an unshielded environment. Our best SQUIDs have a field gradient sensitivity better then 30 fT cm −1 Hz −1/2 . All gradiometers have some response to a homogeneous field, i.e., a parasitic area. The effective pickup area, the field gradient sensitivity, and the components of the parasitic area for the field perpendicular and parallel to the gradiometer plane were measured for all types of gradiometer. The calculations of flux coupling efficiency are compared with experimental results. The origins of parasitic area are discussed. A further reduction of external disturbances was achieved by using an electronic second-order gradiometer. Examples of magnetocardiographic measurement in a physical laboratory without any shielding with first and second-order gradiometers are shown.

As an alternative to the shadow evaporation method for the preparation of ultrasmall tunnel junctions we have established the so-called self-aligned in-line technique. It was applied to the fabrication of common Al/AlO,/Al-type and, for the first time, Nb/AIO,/Nb-based single-electron transistors. The characterization of the samples at temperatures in the range of a few hundred millikelvins reveals charging effects (Coulomb blockade and gate modulation) of the quasiparticle current.

Josephson voltage standards utilize microwave-induced constant voltage steps in the dc characteristic of Josephson tunnel junctions. This paper describes the design and operation of array circuits with 108 and 2000 junctions connected in series. In contrast with similar realizations, simple Q-band equipment is used for the microwave supply. The microwave attenuation of 1000 junctions was about I dB. The version with 2000 junctions generated Josephson voltages up to 1.2 V when operated at 35 GHz. The stability times of the quantized levels were, under normal laboratory conditions (unshielded room), better than 10 mm.

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The current-voltage characteristics and especially the behaviour of the critical Josephson currents of V-V0,-Pb tunnel junctions are investigated experimentally. The maximum Josephson current and its temperature dependence deviate strongly from the theory. The London penetration depth of the vanadium films is found to be much larger than for pure vanadium but its temperature dependence is as expected from theory. The critical temperatures of the vanadium films are between 4.4 and 5.0 K. The ratio 2A(0)/(kFc) decreases with decreasing critical temperature as in the case of superconductors with paramagnetic impurities. The excess currents in the current-voltage characteristics of the tunnel junctions at low voltages are not related to the critical temperatures of the vanadium films. Die Strom-Spannungs-Kennlinien und besonders das Verhalten des kritischen Josephsonstromes von V-V0,-Pb-Tunnelverbindungen werden experimentell untersucht. Der maximale Josephsonstrom und seine TempcraturabhLngigkeit weichen stark von der Theorie ab. Die Londonsche Eindringtiefe der Vanadinschichten ist wesentlich groBer als die fur reines Vanadin, ihre Temperaturabhiingigkeit stimmt jedoch mit der Theorie uberein. Die kritischen Temperaturen der Vanadinschichten liegen zwischen 4,4 und 6,O K. Das Verhaltnis 2A(O)/(kT,) fallt mit abnehmender kritischer Temperatur, wie es fur den Fall eines Supraleiters mit paramagnetischen Verunreinigungen erwartet wid. Die GroBe der VberschuBstrome in den Strom-Spannungs-Kennlinien der Tunnelverbindungen bei geringen Spannungen hangt nicht systematisch von der kritischen Temperatur der Vanadinschichten ab.

The self-aligned in-line technique has been applied to the preparation of ultrasmall low-capacitance metallic tunnel junctions. By using e-beam lithography the area of Al/AlOx/Al contacts has so far been reduced to less than 0.005 μm2. At low temperatures high-ohmic double junctions with a small metallic island between them show the Coulomb blockade effect. The current through such a device could be modulated by a voltage applied to a gate electrode capacitively coupled to the island (single-electron transistor). Both single-charge phenomena have been observed at temperatures up to 1 K.

Studies on superconducting thin films of vanadium for determining the influence of production parameters are performed. The critical temperature Tc is determined as a function of the film thickness and the dependence of the critical magnetic field Hc∥ and Hc⟂ on the reduced temperature is measured. Moreover the dependence of the critical magnetic field and the critical current density on the angle are measured and the film constants λ, ξ, and x are determined. The experimental values are compared with values, which are calculated from the Ginsburg‐Landau theory.