Fluctuations and nonequilibrium thermodynamics in electronic nanosystems

Licentiate thesis, 2022

In the last decades thermodynamics has seen a resurgence because of the interesting phenomena that happen in small-scale systems. Indeed, in nanoscale devices, quantum effects and fluctuations cannot generally be neglected and influence both the transport and their thermodynamic performance. In particular, most devices operate out of equilibrium, where additional fluctuations emerge and nonthermal distributions may occur.
Using the scattering theory formalism, the articles discussed in this thesis contribute to two different aspects of transport in out-of-equilibrium mesoscopic conductors, namely current fluctuations under out-of-equilibrium conditions and the effect of nonequilibrium (or nonthermal) distributions as a resource for thermodynamic operations.
On the one hand, we study the out-of-equilibrium fluctuations in the absence of current, focusing on the shot noise for heat, spin, and charge currents. In particular, we prove the existence of a general bound, namely that, when the zero average charge current is achieved using a temperature and a voltage bias, the charge shot noise is always smaller than the thermal noise.
On the other hand, we introduce a novel quantum transport model to analyze the performance of a hot-carrier solar cell.  This device combines aspects of thermoelectric and photovoltaic devices to enhance its performance. Using our model, we show that exploiting the nonequilibrium resource of a nonthermal distribution improves power production.