Fluctuations are strong in mesoscopic systems and have to be taken into account for the description of transport. We show that they can even be used as a resource for the operation of a system as a device. We use the physics of single-electron tunneling to propose a bipartite device [1,2] working as a thermal transistor [3]. Charge and heat currents in a two terminal conductor can be gated by thermal fluctuations from a third terminal to which it is capacitively coupled. The gate system can act as a switch that injects neither charge nor energy into the conductor hence achieving huge amplification factors. Non-thermal properties of the tunneling electrons can be exploited to operate the device with no energy consumption.
The strong Coulomb interactions typical of quantum dots can furthermore induce rectification effects that lead to thermal diodes in systems with broken mirror symmetry [4].

[1] R. Sánchez, M. Büttiker, Optimal energy quanta to current conversion, Phys. Rev. B 83, 085428 (2011).
[2] H. Thierschmann et al., Three-terminal energy harvester with coupled quantum dots, Nature Nanotech. 10, 854 (2015).
[3] R. Sánchez, H. Thierschmann, L. W. Molenkamp, Phys. Rev. B 95, 241401 (2017), New J. Phys. 19, 113040 (2017).
[4] A. Marcos-Vicioso, C. López-Jurado, M. Ruiz-Garcia, R. Sánchez, arXiv:1803.04073.