High-bandwidth, variable-resistance differential noise thermometry

We develop Johnson noise thermometry applicable to mesoscopic devices with variable source impedance high bandwidth for fast data acquisition. By implementing differential measurement and two-stage matching, we demonstrate in the frequency range 120-250 MHz a wide sample resistance 30 {\Omega}-100 k{\Omega} tuned by gate voltages temperature. employ high-frequency, single-ended low amplifiers maintained at constant cryogenic temperature order maintain desired achieve thermometer calibration precision up 650 mK on 10 K background s of averaging. Using this technique, measure thermal conductivity bilayer graphene spanning metallic semiconducting regimes range, compare it electrical conductivity.