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(a) Simplified schematics of the measurement setup using a resistance bridge circuit and cross correlation of the amplifier signals. (b) Scanning electron micrograph of a shadow-evaporated tunnel junction, with a viewing angle of 60° to the surface normal. The Al leads are widened immediately after the junction to enhance cooling.
Noise spectral density of a sample with junction area from room temperature (topmost trace) to (lowest trace). The data are normalized to the tunnel resistance of the sample. The background was determined by measuring two metal film resistors in bridge configuration.
Noise spectral density of the same sample as in Fig. 1, for between 5 and . At the lowest temperature, a Lorentzian spectrum was fitted to the data.
Temperature dependence of the noise spectral density of five different samples at . The data were normalized to a junction area of . The open (엯) and solid (●) circles are data from the same sample taken in two different cooldowns. The star (⋆) is the average value from Ref. 9 with the dependence (gray line) assumed in that article. The solid black line is a fit to a linear dependence.
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