Shot Noise of a Temperature-Biased Tunnel Junction.

We report the measurement of the current noise of a tunnel junction driven out of equilibrium by a temperature and/or voltage difference, i.e., the charge noise of heat and/or electrical current. This is achieved by a careful control of electron temperature below 1 K at the nanoscale, and a sensitive measurement of noise with wide bandwidth, from 0.1 to 1 GHz. An excellent agreement between experiment and theory with no fitting parameter is obtained. In particular, we find that the current noise of the junction of resistance R when one electrode is at temperature T and the other one at zero temperature is given by S=2 ln2k_{B}T/R.