Development of high frequency and wide bandwidth Johnson noise thermometry

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We develop a high frequency, wide bandwidth radiometer operating at room temperature, which augments the traditional technique of Johnson noise thermometry for nanoscale thermal transport studies.

• Employing low noise amplifiers and an analog multiplier operating at 2~GHz, auto- and cross-correlated Johnson noise measurements are performed in the temperature range of 3 to 300~K, achieving a sensitivity of 5.5~mK (110 ppm) in 1 second of integration time.
• This setup allows us to measure the thermal conductance of a boron nitride encapsulated monolayer graphene device over a wide temperature range.
• Our data shows a high power law (T$^{\sim4}$) deviation from the Wiedemann-Franz law above T$\sim$100~K.