Johnson noise thermometry using ohmic and hydrodynamic electrons

Current through a resistor exhibits temperature-dependent white noise fluctuations called Johnson-Nyquist noise. For a 2D electron system, measuring the magnitude of these fluctuations provides a direct measurement of the electron temperature, and thereby enables a novel method for inferring specific heat and thermal conductivity. Here I present three general theoretical results about Johnson noise thermometry in both the ohmic and hydrodynamic limits. I discuss these in the context of recent and ongoing experiments by the group of Philip Kim, which demonstrate a generalized technique for measuring thermal conductance even of charge-neutral quasiparticles.