Fig. 4
Noise measurement setup and experimental results. a Schematic diagram of noise measurement circuit. Current is injected from source S and the upstream (downstream) noise is measured by a spectrum analyzer through amplifier contact A1 (A2). The contact is connected to an LC circuit at a center frequency f0 = 1.3 MHz, with the signal amplified by a homemade (cooled) voltage pre-amplifier followed by a commercial, room temperature, voltage amplifier (NF-220F5). Note the gain of cold amplifier is taken as 7.5, but the precise gain value was not precisely calibrated. b Upstream excess noise in contact A1 as a function of Is at different magnetic fields. Green line represents the Is-independent (negligible) downstream excess noise at B = 6.1 T
