We report a cryogenic transimpedance amplifier (TA) suitable for cross-correlation current-noise measurements. The TA comprises homemade high-electron-mobility transistors with high transconductance and low noise characteristics, fabricated in an AlGaAs/GaAs heterostructure. The low input-referred noise and wide frequency band of the TA lead to a high resolution in current-noise measurements. The TA’s low input impedance suppresses unwanted crosstalk between two distinct currents from a sample, justifying the advantage of the TA for cross-correlation measurements. We demonstrate the high resolution of a TA-based experimental setup by measuring the shot noise generated at a quantum point contact in a quantum Hall system.
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We observed slight decrease in g at VQPC = −1.28 V (orange asterisk) at V1 < −25 μV (from T↑ = 0.85 to 0.82), suggesting the presence of unintentional impurity scattering near the QPC. Tiny deviations of the noise data from the theoretical curves observed in Figs. 5(c) and 5(d) may be due to such unintentional scatterings, or a slight change in electron temperature during the measurements.
We obtained the value Te = 91 mK from the fit to the cross-correlation data at T↑ = 0.51.