A study of VVOxPb Josephson tunnel junctions

Abstract

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.

High operating temperature in V-based superconducting quantum interference proximity transistors

“…In particular the origin of such large conductance is likely related to the presence of vanadium. Similar high subgap conductances have been observed in several occasions in V-based tunnel junctions 11,18,40,42,44 , as well as in Nb-based tunnel junctions 45 .…”

The influence of vanadium oxide on the properties of Josephson tunnel junctions

“…I T e have to note, however, that the critical temperatures of the electrodes of the junctions and their energy gaps arenot equal. Using relation (6) it is possible to determine the internal field H froin the ratio of the measured I , ( T ) extrapolated to 0 K for V-YO,-Pb junctions [6] to the theoretical value IJO) of Anibegaokar and Baratoff.…”

Characterization of superconducting single-electron transistors with small Al/AlO$_{x}$/V Josephson junctions

“…The voltage range for the original JQP cycle, on the other hand, is expressed in terms of the similar inequality with Δ Al in equation ( 3) being replaced with Δ Δ + Al V [20][21][22][23]. The anomalous superconducting behavior of V-based junctions has been well known since 1960s [28]; it has been considered that surface degradation of the first atomic layer of the deposited V at the interface with the oxide barrier [29] as well as the spin fluctuation effect [30] contributes to a finite QP DOS inside the superconducting gap. We measured transport characteristics of the large reference Al/AlO x /V single junction with = E c 10 μeV in order to study the basic property of the constituent junctions of the SSETs.…”