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3. Results

3.1 Threshold voltage

This section discusses some results from measurements of the threshold voltage Vt on chip H7#43. The array exhibits a sharp nonlinearity where the current jumps from essentially zero to a finite value (figure 5). The experimental definition of Vt is the voltage where the current rises above the noise level, which is of the order of 25 pA.


Figure 5. I-V curve for chip H7#43. Vt is the voltage where the current jumps from zero to a finite value. This curve is taken at lowest temperature (<20 mK) in zero magnetic field in V-bias mode. The curve was swept from low to high voltage. The inset is a magnification of the blockade regime to show the current noise level.

The ramp was run 10 000 times so that several Vt values could be collected and a histogram could be made. Figure 6 displays an example histogram. We discovered that sometimes two or even three peaks appeared in the histograms. The reason for this is unknown.


Figure 6: Example histogram from chip H7#43. This is at B=-0.94 mT, f=19.2 Hz, Vs=85.7 µV and lowest temperature. This histogram has a gaussian distribution and a mean value of about 460 µV.


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